Fix and enable Ruff lints PYI002, PYI026

[intgr]

These affect rest_framework-stubs/compat.pyi which is using some weird hacks that Ruff and mypy don't really like.

• PYI002: If test must be a simple comparison against sys.platform or sys.version_info
• PYI026: Use typing_extensions.TypeAlias for type aliases

Related issues

These were deferred from #488.