ci: fix pipeline run for merge requests

This way CI pipeline runs for branches and tags
and makes it show up in merge requests where
a branch is used as source branch.

Makes all jobs show up in merge request CI
indicator (not just the whitespace job) and
only runs a single CI pipeline, without the
additional detached pipeline.

https://docs.gitlab.com/ce/ci/yaml/#workflowrules-templates

Signed-off-by: Ralph Giles <giles@thaumas.net>

.gitlab-ci.yml

@@ -1,3 +1,6 @@
+include:
+  - template: 'Workflows/Branch-Pipelines.gitlab-ci.yml'
+
 default:
   tags:
     - docker
@@ -6,8 +9,6 @@ default:
 
 whitespace:
   stage: test
-  only:
-    - merge_requests
   script:
     - git diff-tree --check origin/master HEAD