TYP: fix mypy failures on main in pandas/core/generic.py
fixed `mypy` failure on main in `pandas/core/generic.py`:
```
pandas/core/generic.py:6463: error: Argument "deep" to "copy" of "BaseBlockManager" has incompatible type "bool | None"; expected "bool | Literal['all']"  [arg-type]
```
Thanks @natmokval  cc @phofl for the copy typing issue