feat(bkpaas-auth): expand Django version support in tests

[piglei]

Motivation

• Allow projects that depend on bkpaas-auth to upgrade to Django 5.x by relaxing the SDK's dependency bounds.
• Ensure the package is verified against multiple Django major versions via automated matrix testing.
• Avoid CI/test failures caused by strict version pins while keeping compatibility with supported Python versions.

Description

• Bumped bkpaas-auth version to 3.1.4 and relaxed the Django dependency from >=4.2,<5.0 to >=4.2,<6.0 in pyproject.toml.
• Updated noxfile.py to run Django-related tests as a version matrix and added nox.options.error_on_missing_interpreters = False to tolerate missing interpreters; Django 5.x tests are only run on Python >= 3.10.
• Added a changelog entry in CHANGES.md reflecting the Django support change.
• Regenerated poetry.lock metadata to reflect the updated dependency constraints.

Testing

• Ran nox -s tests in sdks/bkpaas-auth to exercise the matrix and test suite under available interpreters.
• Tests passed (51 tests) under the reused Python 3.9 and 3.11 sessions with Django 4.2, and Django 5.x tests passed on Python 3.11.
• The Python 3.10 session failed to create a virtualenv in this environment because the python3.10 interpreter was not available, causing that session to be skipped/failed.
• Executed poetry lock to refresh poetry.lock, which updated the lock file metadata successfully.

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Codex Task