[CI] Start using `was-backported` label (#29239)

.github/workflows/auto-backport.yml

@@ -54,7 +54,7 @@ jobs:
           git checkout master
           git push -u origin ${BACKPORT_BRANCH}
 
-          BACKPORT_PR_URL=$(hub pull-request -b "${TARGET_BRANCH}" -h "${BACKPORT_BRANCH}" -l "auto-backported" -a "${GITHUB_ACTOR}" -F- <<<"🤖 backported \"${ORIGINAL_TITLE}\"
+          BACKPORT_PR_URL=$(hub pull-request -b "${TARGET_BRANCH}" -h "${BACKPORT_BRANCH}" -l "was-backported" -a "${GITHUB_ACTOR}" -F- <<<"🤖 backported \"${ORIGINAL_TITLE}\"
 
           #${ORIGINAL_PULL_REQUEST_NUMBER}")
 

.github/workflows/backport.yml

@@ -111,7 +111,7 @@ jobs:
           if [[ $(hub pr list -b "${TARGET_BRANCH}" -h "${BACKPORT_BRANCH}" -s "open") ]]; then
               echo "PR already exists"
           else
-              BACKPORT_PR_URL=$(hub pull-request -b "${TARGET_BRANCH}" -h "${BACKPORT_BRANCH}" -l "auto-backported" -a "${GITHUB_ACTOR}" -F- <<<"🤖 backported \"${ORIGINAL_TITLE}\"
+              BACKPORT_PR_URL=$(hub pull-request -b "${TARGET_BRANCH}" -h "${BACKPORT_BRANCH}" -l "was-backported" -a "${GITHUB_ACTOR}" -F- <<<"🤖 backported \"${ORIGINAL_TITLE}\"
 
               #${ORIGINAL_PULL_REQUEST_NUMBER}")