drm/ci: pick up -external-fixes from the merge target repo

In case of the merge requests it might be useful to push repo-specific
fixes which have not yet propagated to the -external-fixes branch in the
main UPSTREAM_REPO. For example, in case of drm/msm development, we are
staging fixes locally for testing, before pushing them to the drm/drm
repo. Thus, if the CI run was triggered by merge request, also pick up
the -external fixes basing on the the CI_MERGE target repo / and branch.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Acked-by: Helen Koike <helen.koike@collabora.com>
Link: https://lore.kernel.org/r/20231008132320.762542-1-dmitry.baryshkov@linaro.org
Signed-off-by: Maxime Ripard <mripard@kernel.org>

Author: lumag

drivers/gpu/drm/ci/build.sh

@@ -64,10 +64,15 @@ if [ "$(git ls-remote --exit-code --heads ${UPSTREAM_REPO} ${TARGET_BRANCH}-exte
 fi
 
 # Try to merge fixes from local repo if this isn't a merge request
+# otherwise try merging the fixes from the merge target
 if [ -z "$CI_MERGE_REQUEST_PROJECT_PATH" ]; then
     if [ "$(git ls-remote --exit-code --heads origin ${TARGET_BRANCH}-external-fixes)" ]; then
         git pull origin ${TARGET_BRANCH}-external-fixes
     fi
+else
+    if [ "$(git ls-remote --exit-code --heads ${CI_MERGE_REQUEST_PROJECT_URL} ${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}-external-fixes)" ]; then
+        git pull ${CI_MERGE_REQUEST_PROJECT_URL} ${CI_MERGE_REQUEST_TARGET_BRANCH_NAME}-external-fixes
+    fi
 fi
 
 for opt in $ENABLE_KCONFIGS; do