fix: use mapfile and for loop for branch iteration

Replace process substitution with explicit mapfile to load branches into
an array, then iterate with for loop. This is more reliable in GitHub
Actions bash environment.

Author: alexyaroshuk

.github/workflows/auto-update-prs.yml

@@ -77,7 +77,10 @@ jobs:
           FAILURE_COUNT=0
           SKIPPED_COUNT=0
 
-          while IFS= read -r branch; do
+          # Convert JSON array to bash array
+          mapfile -t BRANCH_ARRAY < <(echo "$BRANCHES" | jq -r '.[]')
+
+          for branch in "${BRANCH_ARRAY[@]}"; do
             [ -z "$branch" ] && continue
 
             echo ""
@@ -108,7 +111,7 @@ jobs:
               git rebase --abort || true
               ((FAILURE_COUNT++))
             fi
-          done < <(echo "$BRANCHES" | jq -r '.[]')
+          done
 
           echo ""
           echo "━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━"