Bump pallets-sphinx-themes from 2.1.1 to 2.1.3 in /requirements (#380)

Bumps [pallets-sphinx-themes](https://github.com/pallets/pallets-sphinx-themes) from 2.1.1 to 2.1.3.
- [Release notes](https://github.com/pallets/pallets-sphinx-themes/releases)
- [Changelog](https://github.com/pallets/pallets-sphinx-themes/blob/main/CHANGES.rst)
- [Commits](pallets/pallets-sphinx-themes@2.1.1...2.1.3)

---
updated-dependencies:
- dependency-name: pallets-sphinx-themes
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/dev.txt

@@ -78,7 +78,7 @@ packaging==23.2
     #   pytest
     #   sphinx
     #   tox
-pallets-sphinx-themes==2.1.1
+pallets-sphinx-themes==2.1.3
     # via -r docs.in
 pip-tools==7.4.1
     # via -r dev.in

requirements/docs.txt

@@ -28,7 +28,7 @@ packaging==21.2
     # via
     #   pallets-sphinx-themes
     #   sphinx
-pallets-sphinx-themes==2.1.1
+pallets-sphinx-themes==2.1.3
     # via -r docs.in
 pygments==2.15.0
     # via