bump the python version used for mac os tests

[bpoldrack]

Same as PR #6286, but against maint

[codecov]

Codecov Report

Merging #6288 (4b597b3) into maint (abcc1ab) will decrease coverage by 2.34%.
The diff coverage is n/a.

❗ Current head 4b597b3 differs from pull request most recent head a455202. Consider uploading reports for the commit a455202 to get more accurate results

@@            Coverage Diff             @@
##            maint    #6288      +/-   ##
==========================================
- Coverage   90.19%   87.85%   -2.35%     
==========================================
  Files         312      312              
  Lines       42272    42254      -18     
==========================================
- Hits        38129    37121    -1008     
- Misses       4143     5133     +990     

Impacted Files	Coverage Δ
datalad/version.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/wtf.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/addurls.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/no_annex.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/add_readme.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/check_dates.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/support/tests/utils.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/export_archive.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/plugin/export_to_figshare.py	0.00% <0.00%> (-100.00%)	⬇️
datalad/metadata/extractors/tests/test_xmp.py	13.63% <0.00%> (-86.37%)	⬇️
... and 93 more

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