.gitlab.ci: Unify CI steps to reduce caching overhead and set CACHE_COMPRESSION_LEVEL: 0

2 jobs for citestbranchtest in 7 minutes and 32 seconds (queued for 5 minutes and 36 seconds)
latest
Status Job ID Name Coverage
  Test
passed #2080
test

00:07:32

failed #2079
test

00:01:38