Add GitHub workflow to test extra compatibility

[yunzheng]

As flow.record still targets Python 3.7 as a minimum, we also test:

• Python 3.7
• Python 3.8
• Windows, Python 3.9+

[codecov[bot]]

Codecov Report

Merging #81 (72ee552) into main (b2818b0) will increase coverage by 0.06%. The diff coverage is n/a.

@@            Coverage Diff             @@
##             main      #81      +/-   ##
==========================================
+ Coverage   79.09%   79.16%   +0.06%     
==========================================
  Files          32       32              
  Lines        2894     2894              
==========================================
+ Hits         2289     2291       +2     
+ Misses        605      603       -2     

Flag	Coverage Δ
unittests	79.16% <ø> (+0.06%)	:arrow_up:

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see 1 file with indirect coverage changes

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