Two coverages unit tests failing under Windows

[pont-us]

Describe the bug

As reported by @forman : two tests in webapi.ows.coverages.test_controllers are failing on Windows (only):

test_get_coverage_datetime_no_time -> Permission error raised in with tempfile.TemporaryDirectory() as tempdir

test_get_coverage_rangetype_for_dataset ->

To Reproduce Steps to reproduce the behavior:

1. Check out current xcube master branch ( c149bcf3293 )
2. Run test suite in a Windows Python environment
3. Observe the two test failures described above

Expected behavior All tests pass.

Additional context Tests pass in CI environments and in a local Linux environment.

[pont-us]

Diagnosis:

• test_get_coverage_datetime_no_time failing due to an unclosed temporary file backing an xr.Dataset, which *nix doesn't care about but Windows does.
• test_get_coverage_rangetype_for_dataset failing due to an underspecified test dataset getting different default dtypes on Linux and Windows.