ci: simplify coverage combining python

a bit more readable, no functionality changes
[skip rhel][skip debian][skip conda][skip integration][skip wheels][skip docker][skip compiler]
6 jobs for coverage-no-swiglal in 40 minutes and 46 seconds (queued for 4 seconds)
Status Job ID Name Coverage
  Tarballs
passed #1215448
tarball:lal

00:00:58

passed #1215447
tarballs

00:06:11

 
  Coverage
passed #1215449
coverage

00:40:46

27.97%
 
  Lint
passed #1215451
lint:coala

00:00:39

passed #1215450
lint:python

00:00:46

 
  Documentation
passed #1215452
documentation

00:05:46