ci: fix backport if condition (#7167)

Can't access secrets from if condition.

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

.github/workflows/backport.yml

@@ -16,15 +16,19 @@ jobs:
   backport:
     name: Backport Pull Request
     if: >
-      secrets.GH_TOKEN_FOR_UPDATES
-      && github.event.pull_request.merged == true
-      && (
-        github.event.action != 'labeled'
+      github.event.pull_request.merged == true &&
+      ( github.event.action != 'labeled'
         || startsWith(github.event.label.name, 'backport')
       )
 
     runs-on: ubuntu-24.04-arm
     steps:
+      - name: Check token
+        run: |
+          if [ -z "${{ secrets.GH_TOKEN_FOR_UPDATES }}" ]; then
+            echo "GH_TOKEN_FOR_UPDATES secret is not set"
+            exit 1
+          fi
       - uses: actions/checkout@v4
         with:
           token: ${{ secrets.GH_TOKEN_FOR_UPDATES }}