Fix and update GitHub Actions + Add publish action

[leifgehrmann]

• Renames the build.yml to test.yml.
• Renames the jobs for existing workflows.
• Added the build.yml workflow to test that python setup.py sdist works.
• Added publish.yml for publishing pangocairocffi.
• Added setuptools to requirements.txt because it is a dependency used in publish.yml and build.yml.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 75.48%. Comparing base (ff494c0) to head (6b2e649).

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #33   +/-   ##
=======================================
  Coverage   75.48%   75.48%           
=======================================
  Files           6        6           
  Lines         155      155           
=======================================
  Hits          117      117           
  Misses         38       38           

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