fix(deps): Update sphinx requirement from ^6.0.0 to >=6,<8 (#255)

Updates the requirements on
[sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest
version.
<details>
<summary>Release notes</summary>
<p><em>Sourced from <a
href="https://github.com/sphinx-doc/sphinx/releases">sphinx's
releases</a>.</em></p>
<blockquote>
<h2>Sphinx 7.1.2</h2>
<p>Changelog: <a
href="https://www.sphinx-doc.org/en/master/changes.html">https://www.sphinx-doc.org/en/master/changes.html</a></p>
</blockquote>
</details>
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/sphinx-doc/sphinx/blob/master/CHANGES.rst">sphinx's
changelog</a>.</em></p>
<blockquote>
<h1>Release 7.1.2 (released Aug 02, 2023)</h1>
<h2>Bugs fixed</h2>
<ul>
<li><a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11542">#11542</a>:
linkcheck: Properly respect :confval:<code>linkcheck_anchors</code>
and do not spuriously report failures to validate anchors.
Patch by James Addison.</li>
</ul>
<h1>Release 7.1.1 (released Jul 27, 2023)</h1>
<h2>Bugs fixed</h2>
<ul>
<li><a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11514">#11514</a>:
Fix <code>SOURCE_DATE_EPOCH</code> in multi-line copyright footer.
Patch by Bénédikt Tran.</li>
</ul>
<h1>Release 7.1.0 (released Jul 24, 2023)</h1>
<h2>Incompatible changes</h2>
<ul>
<li>
<p>Releases are no longer signed, given the <code>change in PyPI
policy</code>_.</p>
<p>.. _change in PyPI policy: <a
href="https://blog.pypi.org/posts/2023-05-23-removing-pgp/">https://blog.pypi.org/posts/2023-05-23-removing-pgp/</a></p>
</li>
</ul>
<h2>Deprecated</h2>
<ul>
<li><a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11412">#11412</a>:
Emit warnings on using a deprecated Python-specific index entry type
(namely, <code>module</code>, <code>keyword</code>,
<code>operator</code>, <code>object</code>, <code>exception</code>,
<code>statement</code>, and <code>builtin</code>) in the
:rst:dir:<code>index</code> directive, and
set the removal version to Sphinx 9. Patch by Adam Turner.</li>
</ul>
<h2>Features added</h2>
<ul>
<li><a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11415">#11415</a>:
Add a checksum to JavaScript and CSS asset URIs included within
generated HTML, using the CRC32 algorithm.</li>
<li>:meth:<code>~sphinx.application.Sphinx.require_sphinx</code> now
allows the version
requirement to be specified as <code>(major, minor)</code>.</li>
<li><a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11011">#11011</a>:
Allow configuring a line-length limit for object signatures, via
:confval:<code>maximum_signature_line_length</code> and the
domain-specific variants.
If the length of the signature (in characters) is greater than the
configured
limit, each parameter in the signature will be split to its own logical
line.
This behaviour may also be controlled by options on object description
directives, for example
:rst:dir:<code>py:function:single-line-parameter-list</code>.</li>
</ul>
<!-- raw HTML omitted -->
</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/320d0b631cc7d9617f5167cc61c9284674f5b2df"><code>320d0b6</code></a>
Bump to 7.1.2 final</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/06c1339bb36378512d2e27bcff86b6bd5db0dc0a"><code>06c1339</code></a>
Ensure that <code>linkcheck_anchors</code> is properly respected (<a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11544">#11544</a>)</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/89808c6f49e1738765d18309244dca0156ee28f6"><code>89808c6</code></a>
Emend attribution for <a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11431">GH-11431</a>
in CHANGES (<a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11547">#11547</a>)</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/4958d2abf1abb1c3a10e77d8297a746cc90d5234"><code>4958d2a</code></a>
Fix flake8 E231 reported linting failure</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/4862da883f8c984e8f15a8643c61702f90947d6c"><code>4862da8</code></a>
Bump version</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/d8d73c16b8b86df8f1a32698229a2b818fea2e98"><code>d8d73c1</code></a>
Bump to 7.1.1 final</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/a54e630a21a6d9b7e80a22e969e3a86e35678d2d"><code>a54e630</code></a>
[internationalisation] Update message catalogues</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/8452300d54dce2da751941d9547dd54dc03e69bf"><code>8452300</code></a>
Fix multi-line copyright when <code>SOURCE_DATE_EPOCH</code> is set (<a
href="https://redirect.github.com/sphinx-doc/sphinx/issues/11524">#11524</a>)</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/fe08cec019c52c15b7f7365013134e3f3d1b3739"><code>fe08cec</code></a>
bump version</li>
<li><a
href="https://github.com/sphinx-doc/sphinx/commit/e560f6334aa87af07304415e6aeaf42d03d1c525"><code>e560f63</code></a>
Bump to 7.1.0 final</li>
<li>Additional commits viewable in <a
href="https://github.com/sphinx-doc/sphinx/compare/v6.0.0...v7.1.2">compare
view</a></li>
</ul>
</details>
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pyproject.toml

@@ -73,7 +73,7 @@ urllib3 = ">=1.22.0,<3"
 optional = true
 
 [tool.poetry.group.docs.dependencies]
-sphinx = "^6.0.0"
+sphinx = ">=6,<8"
 sphinx-rtd-theme = ">=1.3,<3.0"
 certifi = ">=2018.4.16"
 expiringdict = ">=1.1.4"