TYP: fix reportInvalidTypeVarUse from pyright
This fixes the following warning from pyright:  `TypeVar "..." appears only once in generic function signature (reportInvalidTypeVarUse)`.

It would be great to enable pyright on the CI. It takes only ~90sec to run pyright on the entire codebase with the following configuration in pyproject.toml (ignores most type errors for now):
```
[tool.pyright]
pythonVersion = "3.8"
include = ["pandas"]
ignore = ["pandas/tests"]
reportOptionalMemberAccess = false
reportOptionalOperand = false
reportGeneralTypeIssues = false
reportMissingImports = false
reportUnboundVariable = false
reportMissingModuleSource = false
reportOptionalSubscript = false
reportOptionalCall = false
reportOptionalIterable = false
reportPropertyTypeMismatch = false
```
The following errors would need to be taken care of before then:
  pandas/pandas/core/frame.py:4575:9 - error: Method "_reindex_axes" cannot override final method defined in class "NDFrame"
  pandas/pandas/core/frame.py:10736:9 - error: Method "mask" cannot override final method defined in class "NDFrame"
  pandas/pandas/core/series.py:5449:9 - error: Method "mask" cannot override final method defined in class "NDFrame"
  pandas/pandas/core/computation/expr.py:268:26 - error: TypeVar bound type cannot be generic
  pandas/pandas/core/groupby/generic.py:676:9 - error: Method "describe" cannot override final method defined in class "GroupBy"
  pandas/pandas/core/groupby/generic.py:856:9 - error: Method "pct_change" cannot override final method defined in class "GroupBy"