Don't require internet connexion to run configparser tests

[tristanlatr]

fixes #841

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.79%. Comparing base (aee7e81) to head (dfde970).
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #854   +/-   ##
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  Coverage   92.79%   92.79%           
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  Files          47       47           
  Lines        8468     8468           
  Branches     1550     1550           
=======================================
  Hits         7858     7858           
  Misses        350      350           
  Partials      260      260           

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[tristanlatr]

Actually we can now use the upstream version of these parser, which is included in configargparse since version 1.5.5: bw2/ConfigArgParse@v1.5.3...1.5.5 .

The only thing is that the code got merged without the tests, so I'll need to migrate the tests over the configargparse repo first.

Edit: actually since configparser has not received the patch to use the standard library module tomllib, we can’t use it right away. So I’ll merge that and open another issue.