Use deploy key to build Element Enterprise

.github/workflows/build_enterprise.yml

@@ -29,10 +29,15 @@ jobs:
     steps:
       - uses: actions/checkout@v4
         with:
-          submodules: 'true'
           # Ensure we are building the branch and not the branch after being merged on develop
           # https://github.com/actions/checkout/issues/881
           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
+        with:
+          ssh-private-key: ${{ secrets.ELEMENT_ENTERPRISE_DEPLOY_KEY }}
+      - name: Clone submodules
+        run: git submodule update --init --recursive
       - name: Use JDK 17
         uses: actions/setup-java@v4
         with: