Reject plain Concatenate ellipsis annotations

[puneetdixit200]

Fixes #21425.

Summary:

• route Concatenate through the operator path before generic alias handling
• reject direct Concatenate[...] annotations when ParamSpec values are not valid in that location
• add a regression case alongside the existing ParamSpec location checks

Testing:

• python -m mypy -c "from typing import Concatenate; x: Concatenate[...]"
• .venv/bin/python -m pytest mypy/test/testcheck.py::TypeCheckSuite::check-parameter-specification.test -q
• .venv/bin/python -m mypy --config-file mypy_self_check.ini mypy/typeanal.py
• .venv/bin/python runtests.py self
• PATH="$PWD/.venv/bin:$PATH" .venv/bin/python runtests.py lint
• git diff --check

[github-actions]

According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅