Update Python to 3.13.15

[dpy013]

Link to issue number:

Follow on #20589, reopen #20476.

Summary of the issue:

NVDA is currently built and tested with Python 3.13.13. Update the supported Python patch release to Python 3.13.15.

Description of user facing changes:

None.

Description of developer facing changes:

• Update the Python version from 3.13.13 to 3.13.15 for local development, CI, and the 32-bit synth driver runtime builder.
• Update the development environment documentation to reference Python 3.13.15.
• Add a change log entry recording the Python update.

Description of development approach:

Update every current NVDA Python version pin consistently:

• .python-versions
• runtime-builders/synthDriverHost32/.python-version
• GitHub Actions workflows
• projectDocs/dev/createDevEnvironment.md
• user_docs/en/changes.md

The separate miscDeps Python version was intentionally left unchanged because it belongs to its independent build environment.

Testing strategy:

• Confirmed all current NVDA Python version pins use Python 3.13.15.
• Confirmed the CI workflow's default and supported Python versions match.
• Ran git diff --check.
• CI validates the build and test workflows using Python 3.13.15.

Known issues with pull request:

None known.

Code Review Checklist:

• Documentation:
  • Change log entry
  • Developer / Technical Documentation
  • User Documentation: Not applicable; no user-facing behavior changes.
  • Context sensitive help for GUI changes: Not applicable; no GUI changes.
• Testing:
  • Unit tests: Not applicable; configuration-only change.
  • System (end to end) tests: Not run locally; covered by CI.
  • Manual testing: Verified version pins and ran git diff --check.
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
  • No user-facing changes.
• API is compatible with existing add-ons.
• Security precautions taken.