TYP: Ignore remaining mypy errors for pandas\tests\*
- [ ] closes #28926
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry


These are the only 3 errors outstanding in pandas\tests\* that are stopping us closing #28926

```
pandas\conftest.py:301: error: List item 0 has incompatible type "Type[Index]"; expected "Type[PandasObject]"  [list-item]
pandas\tests\window\conftest.py:79: error: List item 0 has incompatible type "ParameterSet"; expected "Sequence[Collection[object]]"  [list-item]
pandas\tests\window\conftest.py:330: error: List item 15 has incompatible type "ParameterSet"; expected "Sequence[Collection[object]]"  [list-item]
```

these appear to be from a mypy inference issue. It maybe best to `# type: ignore[list-item]` just these lines and remove the `ignore_errors=True` from setup.cfg that applies to the whole file for all error codes.

if the mypy error is resolved in a future release, the `warn_unused_ignores = True` in setup.cfg means that we will be alerted and the ignores can be removed.