fix: specify release bound for compat test

[agoose77]

I didn't bisect to find when 3.10 adds the slots argument; I know it's in the release itself, and I don't think we need to be that careful to provide features to old alpha/beta/rc releases.

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[codecov[bot]]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (e717248) 96.07% compared to head (7262cbe) 96.07%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #258   +/-   ##
=======================================
  Coverage   96.07%   96.07%           
=======================================
  Files          62       62           
  Lines        3236     3236           
=======================================
  Hits         3109     3109           
  Misses        127      127           

Flag	Coverage Δ
pytests	96.07% <100.00%> (ø)

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Impacted Files	Coverage Δ
markdown_it/_compat.py	87.50% <100.00%> (ø)

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[chrisjsewell]

Thanks @agoose77, @hukkin wrote this particular part of the code, and so I would suggest he should have a say on this change before merging

[agoose77]

perhaps not worth it to further complicate the tuple comparison

I agree with the principle, but in this case I feel that the extra code is not that much more complex to justify not making this change? I'll defer to your final judgement though — merge this if you're happy, close if not! :)