[FEATURE] Update Numpy 1.20 to 1.21 for mypy

[LovelyBuggies]

We have added types to ndarray, which requires NumPy 1.21 support. We are supposed to make this update for mypy entry in the pre-commit-config.

Probably will hit boost-histogram, too.

[henryiii]

We need:

• np.ndarray -> np.typing.NDArray[Any] (or use the actual DType here)
• Add strings around the expressions in boost-histogram (Hist is okay)
• Bump the version to 1.21 in pre-commit
• Bump the version to 1.14.5 in setup.cfg

[amangoel185]

Fix completed for boost-histogram too with #625 in Boost-histogram.