Enable warnings as errors for weekly run in test suite

[mlxd]

Before submitting

Please complete the following checklist when submitting a PR:

• All new features must include a unit test.
  If you've fixed a bug or added code that should be tested, add a test to the
  test directory!

• All new functions and code must be clearly commented and documented.
  If you do make documentation changes, make sure that the docs build and
  render correctly by running make docs.

• Ensure that the test suite passes, by running make test.

• Add a new entry to the doc/releases/changelog-dev.md file, summarizing the
  change, and including a link back to the PR.

• The PennyLane source code conforms to
  PEP8 standards.
  We check all of our code against Pylint.
  To lint modified files, simply pip install pylint, and then
  run pylint pennylane/path/to/file.py.

When all the above are checked, delete everything above the dashed
line and fill in the pull request template.

---

Context: This PR enables a weekly run of the test suite with Python-level warnings promoted to errors (exceptions). This will allow the test suite to regularly report when hitting warnings through general execution.

Description of the Change: Add a new workflow to run the test suite with Python warnings as errors on a weekly basis,

Benefits: Enable us to catch warnings when and where they occur during testing.

Possible Drawbacks: Additional overhead of running the CI at the intended occurrence.

Related GitHub Issues:

[mudit2812]

Looks good. Left a bunch of suggestions. I would also suggest adding a pull_request trigger to the workflow once it's reasonably complete so you can test it out in action before the PR gets merged.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.29%. Comparing base (a6dabca) to head (ba46b7d).
Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6217   +/-   ##
=======================================
  Coverage   99.29%   99.29%           
=======================================
  Files         457      457           
  Lines       43413    43413           
=======================================
  Hits        43109    43109           
  Misses        304      304           

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

[rashidnhm]

According to GitHub docs fail-fast is a boolean requiring true/false!

Scratch that, this holds true for the current logic in this PR

[rashidnhm]

Thank you for all the work on this!

[mlxd]

Just a note, the accepted suggestions have broken large parts of the action. I intend to roll back to a previous working version, albeit with a more verbose content.