Fix some typing errors in DuckArrayModule

[Illviljan]

Fixes these errors that I've been seeing locally for a while:

!mypy C:\Users\J.W\Documents\GitHub\xarray\xarray\core\coordinates.py --ignore-missing-imports
C:\Users\J.W\Documents\GitHub\xarray\xarray\core\pycompat.py:48: error: Incompatible types in assignment (expression has type "Tuple[]", variable has type "Tuple[Any]")
C:\Users\J.W\Documents\GitHub\xarray\xarray\core\pycompat.py:50: error: Incompatible types in assignment (expression has type "Optional[Module]", variable has type "Optional[Literal['dask', 'pint', 'cupy', 'sparse']]")
Found 2 errors in 1 file (checked 1 source file)

Not sure why the CI isn't catching these?

[headtr1ck]

Good catch, but also no idea why CI didn't catch this. For me locally this was also not catched...

[headtr1ck]

Not sure what is up with minimum version policy and flox but it is unrelated.

[Illviljan]

I think the CI wasn't catching this because of:

xarray/pyproject.toml

Lines 73 to 77 in 63a69fe

	# version spanning code is hard to type annotate (and most of this module will
	# be going away soon anyways)
	[[tool.mypy.overrides]]
	ignore_errors = true
	module = "xarray.core.pycompat"

[headtr1ck]

I think the CI wasn't catching this because of:

xarray/pyproject.toml

Lines 73 to 77 in 63a69fe

	# version spanning code is hard to type annotate (and most of this module will
	# be going away soon anyways)
	[[tool.mypy.overrides]]
	ignore_errors = true
	module = "xarray.core.pycompat"

Since now it seems to work, should we remove the ignore in pyproject.toml?

It seems that this module does mostly handle lazy duck module imports and not python version fixes.

[Illviljan]

Yeah, sounds reasonable. Maybe the reason for the ignore disappeared once DuckArrayModule was implemented?