Rework build system and test execution

This updates C tests to run only as one binary.

The important change is that tests are enabled explicitly and thus in
default disabled. The same now also applies to linters.
8 jobs for rework-tests in 3 minutes and 46 seconds (queued for 5 seconds)
Status Name Job ID Coverage
  Build
passed build-alpine #556321

00:00:44

passed build-debian-stable #556319

00:00:42

passed build-debian-unstable #556320

00:00:41

 
  Test
passed check #556322

00:01:10

passed lint-c #556324

00:00:25

passed lint-lua #556325

00:00:23

passed valgrind-memcheck #556323

00:03:01

 
  Coverage
passed coverage #556326

00:01:18

75.6%