citemplate: tweak merge-request rules

With the MergeRequest rules template, its was impossible
to manually create or trigger a pipeline for a branch/commit
that was not part of a merge request.

This tweaks the workflow:rules such that there will always be
a pipeline for each commit (which will be set to a manual job trigger).

There is the downside that we will now be triggering 2 pipelines in
case of merge requests, but they will require manual action to be
started.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-ci/-/merge_requests/369>

gitlab/ci_template.yml

@@ -1,6 +1,3 @@
-include:
-  - template: 'Workflows/MergeRequest-Pipelines.gitlab-ci.yml'
-
 stages:
   - 'build docker'
   - 'preparation'
@@ -88,6 +85,11 @@ variables:
     --variants werror
     --timestamps
 
+workflow:
+  rules:
+    - if: $CI_MERGE_REQUEST_IID
+    - if: $CI_COMMIT_TAG
+    - if: $CI_COMMIT_BRANCH
 #
 # Global CI policy
 #