Label PRs against target branch, and fail if docs PRs are missing.

Signed-off-by: Leander Stephen D'Souza <leanderdsouza1234@gmail.com>

Author: leander-dsouza

.github/workflows/autotag_docs.yml

@@ -1,33 +1,27 @@
-name: Label docs PRs for ROS Sync
+name: Label docs PRs for backports
 on:
   pull_request:
+    branches:
+      - humble
+      - jazzy
+      - kilted
 
 jobs:
   label-docs:
-    if: contains(github.event.pull_request.title, 'Kilted Sync') || contains(github.event.pull_request.title, 'Jazzy Sync')
     runs-on: ubuntu-latest
     steps:
       - name: Process docs PRs
         env:
-          GH_TOKEN: ${{ github.token }}
+          GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
-          # Determine ROS distro and label from PR title
-          pr_title="${{ github.event.pull_request.title }}"
-
-          if [[ "$pr_title" == *"Kilted Sync"* ]]; then
-            ros_distro="kilted"
-            label="backport-kilted"
-
-          elif [[ "$pr_title" == *"Jazzy Sync"* ]]; then
-            ros_distro="jazzy"
-            label="backport-jazzy"
-          fi
-
           # Get PR numbers from commits
           prs=$(gh api repos/ros-navigation/navigation2/pulls/${{ github.event.number }}/commits \
             --jq '.[].commit.message' | grep -o '#[0-9]\+' | tr -d '#' | sort -u)
 
           # Find and label docs PRs
+          docs_pr_found=false
+          label="backport-${{ github.event.pull_request.base.ref }}"
+
           for pr in $prs; do
 
             # Get cross-referenced events
@@ -38,7 +32,14 @@ jobs:
             if [ -n "$docs_pr" ]; then
               echo "Labeling docs PR #$docs_pr with '$label'"
               gh pr edit $docs_pr --repo ros-navigation/docs.nav2.org --add-label "$label"
+              docs_pr_found=true
             else
               echo "No cross-referenced docs PR found for navigation2 PR #$pr"
             fi
           done
+
+          # Fail if no docs PRs were found
+          if [ "$docs_pr_found" = false ]; then
+            echo "ERROR: No docs PRs found for this backport"
+            exit 1
+          fi