ci: Cope with the fact that the "upstream" remote might already exist

Remove the old "upstream" remote if set, to make sure it points to the
right repo.

.gitlab-ci.yml

@@ -11,7 +11,9 @@ style-check:
         - amd64
     script:
         - git grep -n -P "\t|\r| $" -- . ':(exclude)*/compat/*' && exit 1
-        - git remote add upstream https://code.videolan.org/videolan/dav1d.git && git fetch -q upstream master
+        - git remote rm upstream 2> /dev/null
+        - git remote add upstream https://code.videolan.org/videolan/dav1d.git
+        - git fetch -q upstream master
         - for i in $(git rev-list HEAD ^upstream/master); do
               echo "Checking commit message of $i";
               msg="$(git log --format=%B -n 1 $i)";