Add test for Python 3.11 and support it officially

[jesper-friis]

Description

Also test Python 3.11 and support it officially!

Type of change

• Bug fix.
• New feature.
• Documentation update.
• Test update.

Checklist

This checklist can be used as a help for the reviewer.

• Is the code easy to read and understand?
• Are comments for humans to read, not computers to disregard?
• Does a new feature has an accompanying new test (in the CI or unit testing schemes)?
• Has the documentation been updated as necessary?
• Does this close the issue?
• Is the change limited to the issue?
• Are errors handled for all outcomes?
• Does the new feature provide new restrictions on dependencies, and if so is this documented?

Comments

[codecov]

Codecov Report

Merging #615 (8797844) into master (684e435) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #615   +/-   ##
=======================================
  Coverage   68.14%   68.14%           
=======================================
  Files          16       16           
  Lines        3158     3158           
=======================================
  Hits         2152     2152           
  Misses       1006     1006