[gimp] .gitlab: search common git ancestor with `mr-origin` remote.

[Jehan <jehanp src gnome org>]

commit 1e47c8916ab0bafef010b9ceedfa3cc54fc280dc
Author: Jehan <jehan girinstud io>
Date:   Wed Jan 19 22:17:17 2022 +0100

    .gitlab: search common git ancestor with `mr-origin` remote.
    
    It looks like origin is the same as mr-origin when the contributor
    pushes to one's branch. But when a reviewer rebases through the Gitlab
    "Rebase" button on web GUI, I got a fatal error:
    
    > fatal: ambiguous argument 'origin/asalle/use-dynamics-flag': unknown
      revision or path not in the working tree.
    
    Possibly `origin` is then the remote of the person who rebased (it would
    be weird, yet it's a fact the branch is not found). Let's go with this
    assumption.

 .gitlab/search-common-ancestor.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/.gitlab/search-common-ancestor.sh b/.gitlab/search-common-ancestor.sh
index 7c33309ab5..d5394ffe8f 100644
--- a/.gitlab/search-common-ancestor.sh
+++ b/.gitlab/search-common-ancestor.sh
@@ -30,7 +30,7 @@ git remote add mr-origin ${CI_MERGE_REQUEST_SOURCE_PROJECT_URL}
 source_branch="${CI_MERGE_REQUEST_SOURCE_BRANCH_NAME:-${CI_COMMIT_BRANCH}}"
 git fetch --shallow-since="$(date --date="${ancestor_horizon} days ago" +%Y-%m-%d)" mr-origin 
"${source_branch}" &> ./fetch_origin.log
 
-newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent 
"upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent 
"origin/${source_branch}") | head -1)
+newest_common_ancestor_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list --first-parent 
"upstream/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list --first-parent 
"mr-origin/${source_branch}") | head -1)
 if [ -z "${newest_common_ancestor_sha}" ]; then
     echo "Couldn’t find common ancestor with upstream main branch. This typically"
     echo "happens if you branched from main a long time ago. Please update"