Generate nightly releases on TestPyPI

[dime10]

As part of our ongoing effort to make development across the PennyLane ecosystem easier, this PR introduces nightly releases of the PennyLane package to TestPyPI.

For some context, there has been a strong need for Catalyst development builds to made accessible to PennyLane (and other developers), similar to how PennyLane already depends on Lightning development builds. Beyond helping developers, they are typically needed in order to run CI tasks such as pennylaneAI/qml builds or the compiler tests in this repo.

A complication of this process is that Catalyst itself will usually depend on the development version of PennyLane in order to stay compatible with PL or to get access to recent modifications.
Previously, this has been handled by pointing pip directly to the github repository, e.g. with pip install git+https://github.com/pennylaneai/pennylane@{tag} or pennylane @ git+https://github.com/pennylaneai/pennylane@{tag} in requirement specifications such as setup.py. The latter form is particularly useful because it means a build of catalyst (as a wheel) can automatically fetch the right version of pennylane upon installation (where {tag} is a specific commit on the master branch), providing reproducible builds that will continue to work in the future.
The only problem is that uploading to PyPI is not possible with package dependencies that don't come from PyPI (i.e. GitHub in this case). The proposed solution is to make regular development builds of all PennyLane ecosystem packages available on TestPyPI.

---

This PR introduces a GitHub action that:

• runs every weekday morning on the master branch
• bumps the pennylane package version (e.g. from 0.38.0-dev0 to 0.38.0-dev1)
• builds and uploads a pennylane wheel to TestPyPI

In order to function, we will need to setup trusted publishing on testpypi for this workflow (very easy), a recent feature which bypasses the need for token authentication.

[sc-69108]

[github-actions]

Hello. You may have forgotten to update the changelog!
Please edit doc/releases/changelog-dev.md with:

• A one-to-two sentence description of the change. You may include a small working example for new features.
• A link back to this PR.
• Your name (or GitHub username) in the contributors section.

[mudit2812]

Thanks @dime10 ! Looks good to me. Is there a way to check if the action actually works other than just merging and checking? I guess we could add an "on push" trigger to the action to see if an upload works. If not, we could just merge and pray 😅 .

[dime10]

Thanks @dime10 ! Looks good to me. Is there a way to check if the action actually works other than just merging and checking? I guess we could add an "on push" trigger to the action to see if an upload works. If not, we could just merge and pray 😅 .

Yes we can definitely test it by adding a temporary trigger, which is what I did for the catalyst equivalent. It's a good idea to test once before merging :)
The only problem is that PR actions do not run on a branch (they actually run on a temporary ref that is the merge of the base branch with the pr branch), so the push would fail. But we can comment it out and test the remainder of the action once we have set up trusted publishing on the TestPyPI website. For this we need someone with admin permissions for PennyLane over on PyPI.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.65%. Comparing base (a456fce) to head (d7920df).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6010      +/-   ##
==========================================
- Coverage   99.65%   99.65%   -0.01%     
==========================================
  Files         428      430       +2     
  Lines       41160    41146      -14     
==========================================
- Hits        41020    41005      -15     
- Misses        140      141       +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[mlxd]

Thanks @dime10
One quick change, and then I'm happy to approve