[gjs/native-registry] Fix CI branch finding.

[Evan Welsh <ewlsh src gnome org>]

commit 20b182680fa048473dc3951f68d8ddfb0b038fcc
Author: Evan Welsh <contact evanwelsh com>
Date:   Wed Dec 2 17:04:35 2020 -0600

    Fix CI branch finding.

 test/test-ci.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/test/test-ci.sh b/test/test-ci.sh
index c0ebe9ad..e61c3fe5 100755
--- a/test/test-ci.sh
+++ b/test/test-ci.sh
@@ -35,7 +35,7 @@ do_Get_Upstream_Base () {
     # should probably be rebased.
     git remote add upstream https://gitlab.gnome.org/GNOME/gjs.git || \
         git remote set-url upstream https://gitlab.gnome.org/GNOME/gjs.git
-    base_branch="${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}"
+    
base_branch="${CI_EXTERNAL_PULL_REQUEST_SOURCE_BRANCH_NAME:-${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH:-${CI_DEFAULT_BRANCH}}}}"
     git fetch --shallow-since="14 days ago" --no-tags upstream "$base_branch"
     git branch ci-upstream-base-branch FETCH_HEAD