add twine_check to "tox -e lint" and CI

[jquast]

For final README.rst and packaging metadata linting

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cf17c98) to head (feb4a7a).

Additional details and impacted files

@@            Coverage Diff            @@
##            master      #236   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           27        27           
  Lines         1976      1976           
  Branches       463       463           
=========================================
  Hits          1976      1976           

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[codspeed-hq]

Merging this PR will not alter performance

✅ 108 untouched benchmarks

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_{Comparing jq/twine-check (feb4a7a) with master (cf17c98)}