Fix error message for type application on non-generic expressions

[achbj]

Summary

Update the error message "Type application is only supported for generic classes" to also mention type aliases, since type application is also valid for generic type aliases.

The original error message was misleading because it stated that type application is only supported for generic classes, but type aliases also support type application (e.g., type TA[T] = list[T]; v: TA[int] works correctly).

Changes

• Updated ONLY_CLASS_APPLICATION error message in mypy/message_registry.py from "Type application is only supported for generic classes" to "Type application is only supported for generic classes and type aliases"
• Updated corresponding test expectations in:
  • test-data/unit/check-generics.test
  • test-data/unit/check-parameter-specification.test
  • test-data/unit/check-typevar-tuple.test

Test plan

• Ran pytest mypy/test/testcheck.py::TypeCheckSuite::check-generics.test - all 194 tests passed
• Ran pytest mypy/test/testcheck.py::TypeCheckSuite::check-parameter-specification.test - tests passed
• Ran pytest mypy/test/testcheck.py::TypeCheckSuite::check-typevar-tuple.test - tests passed
• Manually verified the fix with a test file

🤖 Generated with Claude Code

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

Tanjun (https://github.com/FasterSpeeding/Tanjun)
- tanjun/commands/menu.py:63: error: Type application is only supported for generic classes  [misc]
+ tanjun/commands/menu.py:63: error: Type application is only supported for generic classes and type aliases  [misc]