Relax Docker test severity and fix remaining issues

3 jobs for tests in 50 seconds (queued for 1 second)
Status Job ID Name Coverage
  Test
passed #39438
dockerfiles

00:00:33

failed #39437
allowed to fail
shellcheck

00:00:26

failed #39439
allowed to fail
yamllint

00:00:23

 
Name Stage Failure
failed
yamllint Test
No job log
failed
shellcheck Test
No job log