circleci: ignore gitlab branches for all jobs in the validate workflow

Authored by alpmestan on Dec 11 2018, 12:11 PM.

Description

circleci: ignore gitlab branches for all jobs in the validate workflow

Our previous attempt ended up breaking the CircleCI config, but
this one has been tested, see:

https://circleci.com/gh/ghc/ghc/tree/alp%2Fcircleci%2Fignore-gitlab-branches

which shows the builds getting triggered correctly. I also pushed the same
branch under 'gitlab/alp/test', and that didn't trigger any build, as desired.

Reviewers: bgamari

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5429

Details