Fix Python 3.10 tests

[pquentin]

There was a change in CPython that broke pytest. pytest-dev/pytest#8540 fixed it, which is why I bumped it but pytest was not relased, so that did not help. But it does not hurt either, so I left the version bumps.

The issue appeared since GitHub Actions released a "beta 1" CPython 3.10, which is weird since the actual beta 1 is not out yet, but this is what 3.10-dev now refers to. See pytest-dev/pytest#8540 (comment).

So the fix is to pin to alpha 7, and when pytest gets relased we'll unpin Python 3.10 and bump pytest.

[codecov]

Codecov Report

Merging #2201 (fc2244f) into main (287052a) will not change coverage.
The diff coverage is n/a.

❗ Current head fc2244f differs from pull request most recent head 6e00a5b. Consider uploading reports for the commit 6e00a5b to get more accurate results

@@            Coverage Diff            @@
##              main     #2201   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           24        24           
  Lines         2219      2219           
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  Hits          2219      2219           

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