Fixes a bug that breaks virtual modules on Windows

[seifertm]

pytest-asyncio v0.23.4a0 introduced "virtual modules". These are temporary files in Python packages which contain a fixture definition. The files are removed after the virtual module was collected by pytest.

The use of temporary files has platform-specific behavior. Apparently, pytest opens the NamedTemporaryFile again, which causes issues on Windows. The the docs describe the problem and possible mitigations:

Opening the temporary file again by its name while it is still open works as follows:
On POSIX the file can always be opened again.
On Windows, make sure that at least one of the following conditions are fulfilled:
* delete is false
* additional open shares delete access (e.g. by calling os.open() with the flag O_TEMPORARY)
* delete is true but delete_on_close is false. Note, that in this case the additional opens that do not share delete access (e.g. created via builtin open()) must be closed before exiting the context manager, else the os.unlink() call on context manager exit will fail with a PermissionError.

The delete_on_close flag has only been added in Python 3.12, so pytest-asyncio cannot use it at the moment. Neither does pytest-asyncio have the means to influence how pytest opens a file for collection. This leaves us with setting delete=False in the constructor of the NamedTemporaryFile and clean it up manually.

This PR also enabled CI tests on Windows to reproduce the problem (and validate the fix).

See #729

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (aecfd01) 94.76% compared to head (705f745) 94.78%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #746      +/-   ##
==========================================
+ Coverage   94.76%   94.78%   +0.02%     
==========================================
  Files           2        2              
  Lines         497      499       +2     
  Branches       99       99              
==========================================
+ Hits          471      473       +2     
  Misses         19       19              
  Partials        7        7              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.