Drop retired Python 3.5

[amureki]

Description of the Change

Python 3.5 did reach end-of-life in September 2020:
https://www.python.org/downloads/release/python-3510/

We can safely remove it from CI to reduce test running time.

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS

[codecov]

Codecov Report

Merging #936 (4415928) into master (d6d1f99) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #936   +/-   ##
=======================================
  Coverage   94.94%   94.94%           
=======================================
  Files          30       30           
  Lines        1423     1423           
=======================================
  Hits         1351     1351           
  Misses         72       72           

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[amureki]

There is a funny artefact:

build (3.5) Expected — Waiting for status to be reported

I don't think it is coming from code, but rather something was cached or so.

Also, I noticed that GH Actions are running twice, I took an opportunity to fix it in a separate PR: #937

[n2ygk]

Thanks!

[n2ygk]

@MattBlack85 @jezdez Do you know how we "unstick" this expected build (3.5)? This PR removes py35. I believe this has to be removed from the protect branch settings.

[jezdez]

@jezdez Do you know how we "unstick" this expected build (3.5)? This PR removes py35. I believe this has to be removed from the protect branch settings.

Yeah, no problem, I removed the branch protection for the 3.5 build.