Only add private SSH keys and clone submodules in the original repo (#3225)

.github/workflows/tests.yml

@@ -40,6 +40,7 @@ jobs:
           ref: ${{ github.event_name == 'pull_request' && github.event.pull_request.head.sha || github.ref }}
       - name: Add SSH private keys for submodule repositories
         uses: webfactory/ssh-agent@v0.9.0
+        if: github.repository == 'element-hq/element-x-android'
         with:
           ssh-private-key: ${{ secrets.ELEMENT_ENTERPRISE_DEPLOY_KEY }}
       - name: Clone submodules