gitlab: Don't run lint-submods job on Marge branches
gitlab: Don't run lint-submods job on Marge branches

This broke Marge by creating a second pipeline (consisting of only the
`lint-submods` job). Marge then looked at this pipeline and concluded
that CI for her merge branch passed. However, this is ignores the fact
that the majority of the CI jobs are triggered on `merge_request` and
are therefore in another pipeline.

sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc,sdiehl/ghc