.gitlab-ci.yml: move coverage analysis to the end, set it manual

See #3339. We want to have first fast tests.
Once we will have #3340, we will run again always this stage.
9 jobs for feature-a/3339-coverage-stage in 32 minutes and 17 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test Tools
passed #130090
test_tools

00:00:04

 
  Test Unit
passed #130091
test_algo_unit

00:02:24

passed #130092
test_tools_unit

00:00:05

 
  Test Functional
passed #130093
test_algo_should

00:09:31

 
  Test Shouldvdj
passed #130094
test_algo_shouldvdj

00:09:30

 
  Prepare Release
manual #130095
allowed to fail manual
prepare_release
 
  Valgrind Unit
passed #130096
valgrind
algo_valgrind_unit

00:10:45

 
  Valgrind Functional
manual #130097
valgrind allowed to fail manual
algo_valgrind_functional
 
  Coverage
manual #130098
allowed to fail manual
algo_coverage