Skip tests using util on Python 3.15 alpha/beta.

[junkmd]

Related to #938.

Temporarily skip tests relying on util when running on Python 3.15 alpha/beta versions, as recent layout changes cause a RuntimeError during import.

[junkmd]

The CI error ("gpg: Can't check signature: No public key" in "Upload coverage reports to Codecov") matches reports in:

• GPG public key import returns invalid OpenPGP data, blocking Codecov uploads codecov/codecov-action#1955

I'll keep an eye on the issue and re-run CI once a fix or workaround is available.

[codecov-commenter]

⚠️ Please install the to ensure uploads and comments are reliably processed by Codecov.

Codecov Report

❌ Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.93%. Comparing base (8fec088) to head (f1b2802).

Files with missing lines	Patch %	Lines
comtypes/test/test_util.py	40.00%	6 Missing ⚠️
❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #939      +/-   ##
==========================================
- Coverage   88.98%   88.93%   -0.06%     
==========================================
  Files         139      139              
  Lines       13633    13642       +9     
==========================================
+ Hits        12132    12133       +1     
- Misses       1501     1509       +8     

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[junkmd]

With the update mentioned in codecov/codecov-action#1956 (comment), it is now possible to upload coverage artifacts and integrate with GitHub while using codecov-action@v5.

Given the evolving threat model of supply chain attacks within the open-source ecosystem, it may be necessary to improve the content of this project's workflow files in the future.
However, I believe this would be addressed in a separate issue scope rather than all at once in this PR.