Fix instance update commit as gh-bot

.github/workflows/update-instances.yml

@@ -10,6 +10,12 @@ jobs:
     - uses: actions/checkout@v2
     - name: Install dependencies
       run: sudo apt-get install -y jq
+
+    - uses: webfactory/ssh-agent@v0.5.3
+      with:
+        ssh-private-key: |
+          ${{ secrets.PRIMARY_REPO_KEY }}
+
     - name: Fetch instances
       run: |
         function apply_update() {