Self-hosted runner cleanup: run only in GfW org

It doesn't make sense to run this scheduled job on forks, because they don't have the required secrets.

Signed-off-by: Dennis Ameling <dennis@dennisameling.com>

Author: dennisameling

.github/workflows/cleanup-self-hosted-runners.yml

@@ -17,6 +17,7 @@ on:
 #                        group specifically for self-hosted Actions Runners.
 jobs:
   delete-runner:
+    if: github.repository_owner == 'git-for-windows'
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v4