Test on Python 3.9-dev to avoid surprises

[hugovk]

Python 3.9 is in alpha, with beta in May and full release in October.

• https://www.python.org/dev/peps/pep-0596/

[codecov-io]

Codecov Report

Merging #438 into master will not change coverage.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           master    #438   +/-   ##
======================================
  Coverage    90.6%   90.6%           
======================================
  Files          50      50           
  Lines        6983    6983           
  Branches     1328    1328           
======================================
  Hits         6327    6327           
  Misses        497     497           
  Partials      159     159

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[FelixSchwarz]

just wanted to add that testing the latest CPython version would be also good for Fedora. We are updating to new Python releases pretty quickly and CPython changed to an annual release cycle which fits better for Linux distros like Fedora.

Most packagers will report errors found during the mass rebuilds when transitioning to new CPython releases but of course it would be much more efficient if these were spotted upstream. :-)

[codecov-commenter]

Codecov Report

Merging #438 into master will increase coverage by 0.05%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #438      +/-   ##
==========================================
+ Coverage   90.94%   90.99%   +0.05%     
==========================================
  Files          49       49              
  Lines        6933     6933              
  Branches     1321     1321              
==========================================
+ Hits         6305     6309       +4     
+ Misses        471      467       -4     
  Partials      157      157              

Impacted Files	Coverage Δ
html5lib/tests/support.py	93.96% <0.00%> (+1.72%)	⬆️
html5lib/_utils.py	87.50% <0.00%> (+3.12%)	⬆️

---

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