ci: fix Python package in coverage workflow

[striezel]

Description

This pull request fixes the E: Package 'python' has no installation candidate error in the coverage workflow by providing an existing package.

The Python package in Ubuntu 22.04 is python3, but I decided to go for python-is-python3 instead, because that makes sure that python3 is installed (as dependency) and also creates a symlink from /usr/bin/python to python3 as a way to make sure that commands with just python (instead of python3) also invoke the installed version of Python 3.

References

See https://github.com/boostorg/gil/actions/runs/7317309558/job/19932692704 for an example of a currently failing coverage job.

Tasklist

• Ensure all CI builds pass
• Review and approve

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (1df8c24) 81.10% compared to head (8888bf5) 82.12%.
Report is 7 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #740      +/-   ##
===========================================
+ Coverage    81.10%   82.12%   +1.02%     
===========================================
  Files          117      117              
  Lines         5171     5355     +184     
===========================================
+ Hits          4194     4398     +204     
+ Misses         977      957      -20     

[mloskot]

Thank you!