CI: ignore some warnings

[mathause]

• Part of Warnings in the test suite #3266
• Passes isort . && black . && mypy . && flake8

Supresses 3 warnings we get in the test suite. Two are trivial. The third is PytestUnraisableExceptionWarning: Exception ignored in: CachingFileManager.__del__:

• The test triggers an error is in CachingFileManager.__init__:

xarray/xarray/tests/test_backends_file_manager.py

Lines 205 to 207 in 31d540f

	def test_file_manager_invalid_kwargs():
	with pytest.raises(TypeError):
	CachingFileManager(open, "dummy", mode="w", invalid=True)

• It then tries to run __del__ but there is an error because an attribute is not available (as __init__ failed)

xarray/xarray/backends/file_manager.py

Line 238 in 31d540f

ref_count = self._ref_counter.decrement(self._key)

• However, errors in __del__ are ignored, therefore we get a PytestUnraisableExceptionWarning

I decided to suppress the error and not fix CachingFileManager as I think that's nothing user-facing...

[keewis]

I wonder why we have that test at all: we don't accept invalid or **kwargs as a parameter, which means that the TypeError is raised by the interpreter.

Edit: maybe the intention was to pass kwargs={"invalid": True}?

[mathause]

I wonder why we have that test at all

Good point, thanks! When the test was written CachingFileManager had a **keywords argument. This is no longer the case so I'll remove the test.