[5.1] chore(ci): update github workflow actions to latest versions

[phil-davis]

and pin cs-fixer to 3.64.0

3.65.0 complains about some small code things (a mention of \Generator), and we don't want to adjust that in 5.1, because 5.1 supports earlier PHP7.1 7.2 7.3 that use an older cs-fixer that does not complain.

This gets the CI passing again in the 5.1 branch, in case we need to fix and release some real code in the future.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.73%. Comparing base (25a3020) to head (414fb2b).
⚠️ Report is 3 commits behind head on 5.1.

Additional details and impacted files

@@            Coverage Diff            @@
##                5.1     #140   +/-   ##
=========================================
  Coverage     99.72%   99.73%           
+ Complexity      118      109    -9     
=========================================
  Files             7        7           
  Lines           365      375   +10     
=========================================
+ Hits            364      374   +10     
  Misses            1        1           

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