ci: Update dependabot-approve-merge.yml

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

.github/workflows/dependabot-approve-merge.yml

@@ -31,6 +31,12 @@ jobs:
       pull-requests: write
 
     steps:
+      - name: Disabled on forks
+        if: ${{ github.event.pull_request.head.repo.full_name != github.repository }}
+        run: |
+          echo 'Can not approve PRs from forks'
+          exit 1
+
       # GitHub actions bot approve
       - uses: hmarr/auto-approve-action@b40d6c9ed2fa10c9a2749eca7eb004418a705501 # v2
         with: