[mutter] ci: Fetch the right target branch

[Marge Bot <marge-bot src gnome org>]

commit 264c625b79e085b6282e4f5f71901d9f59aa376c
Author: Robert Mader <robert mader posteo de>
Date:   Tue Aug 24 11:16:10 2021 +0200

    ci: Fetch the right target branch
    
    And remove a superfluous fallback to the default branch - we already
    check that the target branch is defined.
    
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1973>

 .gitlab-ci.yml | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index 697c71f053..50400e7363 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -151,8 +151,8 @@ check-code-style:
   script:
     - if [[ x"$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" != "x" ]] ;
       then
-        git fetch origin master;
-        export common_parent_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list 
--first-parent "origin/${CI_MERGE_REQUEST_TARGET_BRANCH_NAME:-${CI_DEFAULT_BRANCH}}") <(git rev-list 
--first-parent HEAD) | head -1) ;
+        git fetch origin $CI_MERGE_REQUEST_TARGET_BRANCH_NAME ;
+        export common_parent_sha=$(diff --old-line-format='' --new-line-format='' <(git rev-list 
--first-parent "origin/$CI_MERGE_REQUEST_TARGET_BRANCH_NAME") <(git rev-list --first-parent HEAD) | head -1) ;
         python3 -u ./check-style.py --dry-run --sha $common_parent_sha ;
       else
         echo "Not a merge request" ;