Enable reporting of encoding warnings.

[jaraco]

Description

As suggested in #561 and #577, enable reporting of EncodingWarnings per PEP 597.

This PR is proposed separately from #577, because #577 only fixes the warnings in the main codebase and not in the tests. 80-some warnings remain to be addressed, so I leave it to the maintainers to determine when to add this check.

Checklist

• Make sure changes are covered by existing or new tests.
• For at least one Python version, make sure local test run is green.
• Create a file in src/towncrier/newsfragments/. Describe your
  change and include important information. Your change will be included in the public release notes.
• Make sure all GitHub Actions checks are green (they are automatically checking all of the above).
• Ensure docs/tutorial.rst is still up-to-date.
• If you add new CLI arguments (or change the meaning of existing ones), make sure docs/cli.rst reflects those changes.
• If you add new configuration options (or change the meaning of existing ones), make sure docs/configuration.rst reflects those changes.

[adiroiban]

Thansk for the PR... sorry for missing it.

Feel free to ping me if a PR is not reviewed.

I sent invitation to you and @SmileyChris to towncrier contributors team... if a PR is approved, you can trigger the merge.

[adiroiban]

Thanks.

We can have it merged.

The current change will not do much in our CI... but I hope that it will make problem more visible to the current dev team :)

I think that this is something that we might to have in trial.

Trial should capture the warnings and fail on warnings

[adiroiban]

I have enabled auto-merge for this. I hope it will land soon. Thanks again!