chore(api): Update testnet deploy CI

Author: rohanjadvani

.github/workflows/deploy-testnet.yml

@@ -12,7 +12,10 @@ jobs:
     steps:
       - name: Check out Git repository
         uses: actions/checkout@v2
-      - uses: akhileshns/[email protected]
+      - name: Install Heroku CLI
+        run: |
+          curl https://cli-assets.heroku.com/install.sh | sh 
+      - uses: akhileshns/[email protected]
         with:
           heroku_app_name: ${{ secrets.HEROKU_APP_NAME_TESTNET }}
           heroku_api_key: ${{ secrets.HEROKU_API_KEY }}