CI: Run fewer jobs on wip/ branches

If the branch is marked with wip/, then we should only run one build/test
job, just to make sure the tests pass; we don't need to do it with two
different compilers. Also, skip the code coverage job on wip/ branches.
4 jobs for faster-ci in 14 minutes and 27 seconds (queued for 1 second)
Status Job ID Name Coverage
  Static Analysis
passed #7164
cppcheck

00:00:26

 
  Build
passed #7165
fedora_gcc

00:02:52

 
  Thorough Tests
passed #7166
coverage

00:11:08

 
  Failure
skipped #7167
on_failure