Merge branch 'ux/suppress-ci-yml-warning' into 'master'

Suppress warning about missing `.gitlab-ci.yml` if builds are disabled

When user disables GitLab Ci Service in project's settings then warning
about missing `.gitlab-ci.yml` file should be supressed. This a matter
of user experience as stated in #3761 (closes #3761).

cc @ayufan 

See merge request !2014