Support Python 3.14: classifiers, docs, and CI matrix fix

[DivInstance]

This PR addresses issue #298 by completing Python 3.14 support:

• Add Programming Language Python 3.14 classifier in setup.py.
• Update docs docs/index.rst to say “supports CPython 3.9 up to 3.14”.
• Fix a CI workflow typo so job python-version uses matrix.config[0], ensuring 3.14 runs as intended.
• Note these changes under “8.1 (unreleased)” in CHANGES.rst.

[dataflake]

I appreciate the PR, but part of it will need reworking because .github/workflows/tests.yml is template-generated by zope.meta and any fixes need to be made there before re-running template generation here. There also has not been a security audit to identify changes in Python 3.14 that require work in RestrictedPython.

[dataflake]

The typo in the tests.yml configuration is now fixed in zope.meta and applied here. Thanks for catching that.

I have to reject the rest of this PR, though. It does not address issue #298 because it seems to omit the most important step before declaring Python 3.14, a security audit into the changes from 3.13 to determine if any further changes need to be made in RestrictedPython.

[DivInstance]

Acknowledge the typo fix; will pursue a proper 3.14 security audit (issue #298) with a concrete plan and a dedicated PR before updating classifiers/docs/CI to declare official support. Thank you for your feedback.

[dataflake]

Don't forget that in order to accept a PR you must sign the Zope contributor agreement. This can be done electronically. See https://www.zope.dev/developer/becoming-a-committer.html for details.