Use GitHub Actions for x86_64 tests

[mayeut]

Move to GHA in order to save some travis-ci credits on the pypa account.
xref pypa/packaging#395, pypa/manylinux#988

[codecov]

Codecov Report

Merging #282 (01667eb) into master (686024e) will decrease coverage by 1.85%.
The diff coverage is 92.10%.

@@            Coverage Diff             @@
##           master     #282      +/-   ##
==========================================
- Coverage   90.89%   89.03%   -1.86%     
==========================================
  Files          20       20              
  Lines        1043     1058      +15     
  Branches      223      226       +3     
==========================================
- Hits          948      942       -6     
- Misses         54       69      +15     
- Partials       41       47       +6     

Impacted Files	Coverage Δ
auditwheel/main_lddtree.py	72.72% <ø> (ø)
auditwheel/policy/versioned_symbols.py	92.30% <ø> (ø)
auditwheel/condatools.py	91.66% <75.00%> (-8.34%)	⬇️
auditwheel/wheeltools.py	87.02% <78.94%> (-4.98%)	⬇️
auditwheel/elfutils.py	93.82% <100.00%> (ø)
auditwheel/genericpkgctx.py	50.00% <100.00%> (+5.55%)	⬆️
auditwheel/hashfile.py	100.00% <100.00%> (ø)
auditwheel/lddtree.py	92.19% <100.00%> (-0.71%)	⬇️
auditwheel/main.py	100.00% <100.00%> (ø)
auditwheel/main_addtag.py	65.78% <100.00%> (-21.06%)	⬇️
... and 13 more

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