Try giving it option user.

Author: cindytsai

.github/workflows/deploy_gcp.yml

@@ -25,6 +25,8 @@ jobs:
         uses: 'google-github-actions/ssh-compute@v1'
         with:
           instance_name: 'instance-1'
+          project_id: 'deepgit'
+          user: "user"
           zone: 'us-central1-f'
           ssh_private_key: '${{ secrets.GCP_SSH_PRIVATE_KEY }}'
           command: 'echo Hello world'