[4.6] Publish GitHub release notes after deployment

[nicoddemus]

Backport of the following PRs: #5723, #5740, and #5750.

[codecov]

Codecov Report

Merging #5767 into 4.6-maintenance will increase coverage by 0.24%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##           4.6-maintenance    #5767      +/-   ##
===================================================
+ Coverage            95.92%   96.17%   +0.24%     
===================================================
  Files                  115      115              
  Lines                26553    26553              
  Branches              2615     2615              
===================================================
+ Hits                 25472    25537      +65     
+ Misses                 755      710      -45     
+ Partials               326      306      -20

Impacted Files	Coverage Δ
src/_pytest/unittest.py	93.22% <0%> (-1.05%)	⬇️
testing/test_pdb.py	99.02% <0%> (+0.19%)	⬆️
src/_pytest/fixtures.py	97.55% <0%> (+0.27%)	⬆️
testing/test_capture.py	99.25% <0%> (+0.29%)	⬆️
testing/test_terminal.py	99.84% <0%> (+0.31%)	⬆️
testing/test_config.py	99.83% <0%> (+0.32%)	⬆️
src/_pytest/pytester.py	91.66% <0%> (+0.42%)	⬆️
src/_pytest/assertion/rewrite.py	95.77% <0%> (+0.48%)	⬆️
testing/python/fixtures.py	99.09% <0%> (+0.56%)	⬆️
src/_pytest/junitxml.py	95.9% <0%> (+0.58%)	⬆️
... and 11 more

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[nicoddemus]

Had to stop upgrading pip due to it failing on py34 (9191857):

Requirement already up-to-date: pip in c:\hostedtoolcache\windows\python\3.4.4\x64\lib\site-packages (19.2.1)
ERROR: Package 'pip' requires a different Python: 3.4.4 not in '>=2.7,!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*'
[error]Cmd.exe exited with code '1'.

Link: https://pytest-dev.visualstudio.com/pytest/_build/results?buildId=2062

[nicoddemus]

Travis failed due to coverage being down.

Because Travis passed in the previous commit, and the last commit only touched azure-pipelines.yaml I'm assuming this is temporary so I'm going ahead with the merge.