Update Cython version used in pyproject.toml

[astrofrog]

I think this might fix some of the Windows CI issues

[codecov]

Codecov Report

Merging #337 (6af66c6) into main (91034a7) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #337   +/-   ##
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  Coverage   91.86%   91.86%           
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  Files          33       33           
  Lines        2508     2508           
=======================================
  Hits         2304     2304           
  Misses        204      204           

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[larrybradley]

The test failures look real. TestEllipsePixelRegion.test_as_mpl_selector is expecting a center of 8.3, but getting 5.0.
https://dev.azure.com/astropy-project/regions/_build/results?buildId=1146&view=logs&j=7f33e5bd-7764-5d8a-ba2e-506e078b9c3f&t=57e5be12-0a85-50b9-0e83-1cf5152ef732&l=218

[astrofrog]

I wonder if this is related to some changes in Matplotlib

[astrofrog]

I can't reproduce the issue locally, I wonder whether there is some kind of race condition in the interactivity or if we somehow need to force everything to be drawn before checking values.

[astrofrog]

This does fix the docs build which had the Cython issues though so going to merge this and we should investigate the selector test issues separately (these happen even without the Cython upgrade)