ci: only protected branches should have PULL_REQUEST set to false

.gitlab-ci.yml

@@ -95,14 +95,16 @@ builder-image:
       else
         # CI_EXTERNAL_PULL_REQUEST_IID is false every time until https://gitlab.com/gitlab-org/gitlab/issues/5667 is done
         # Until then, we're using https://github.com/brndnmtthws/labhub atm to mirror Github pull requests as branches into Gitlab,
-        # which allows us to use Gitlab CI for Github. The following check detects such mirrored branches.
-        if [[ $CI_COMMIT_REF_NAME =~ ^pr-[^/]*/[^/]*/[^/]*/[^/]*$ ]]; then
+        # which allows us to use Gitlab CI for Github.
+        if [[ $CI_COMMIT_REF_NAME = "master" ]] || [[ $CI_COMMIT_REF_NAME = "develop" ]] || [[ $CI_COMMIT_REF_NAME =~ ^v([0-9]{1,2}\.)*x$ ]]; then
+          # These names are reserved for protected branches
+          export PULL_REQUEST="false"
+        else
+          # Everything else including experemental "feat/smth" branches must be merged via PRs
           export PULL_REQUEST="true"
           # CI_COMMIT_BEFORE_SHA is also invalid until #5667 is implemented, so we need to figure it out by ourself
           git fetch origin develop
           export CI_COMMIT_BEFORE_SHA="$(git merge-base origin/develop HEAD)"
-        else
-          export PULL_REQUEST="false"
         fi
       fi
     - export COMMIT_RANGE="$CI_COMMIT_BEFORE_SHA..$CI_COMMIT_SHA"