Can't deploy container to GCE, using gcloud compute instances update-container, because of YML parse error

name: Build and Deploy to Google Compute Engine (one more time, yes)

on:
  push:
    branches:
    - 'main'

env:
  PROJECT_ID: ***
  GCE_INSTANCE: ***
  GCE_INSTANCE_ZONE: ***

jobs:
  setup-build-publish-deploy:
    name: Setup, Build, Publish, and Deploy
    runs-on: ubuntu-latest

    # Add "id-token" with the intended permissions.
    permissions:
      contents: 'read'
      id-token: 'write'

    steps:
    # Checkout Action
    - name: Checkout
      uses: actions/checko[email protected]

    # Authentication via credentials json
    - id: 'auth'
      uses: 'google-github-actions/[email protected]'
      with:
        credentials_json: '${{ secrets.GCP_SA_KEY }}'

    # Setup gcloud CLI
    - name: Set up Cloud SDK
      uses: google-github-actions/[email protected]

    # Configure Docker to use the gcloud command-line tool as a credential helper for authentication
    - run: |-
        gcloud --quiet auth configure-docker
    
    # Build the Docker image
    - name: Build
      run: |-
        docker build --tag "gcr.io/$PROJECT_ID/$GCE_INSTANCE-image:$GITHUB_SHA" ./path/to/Dockerfile
    
    # Push the Docker image to Google Container Registry
    - name: Publish
      run: |-
        docker push "gcr.io/$PROJECT_ID/$GCE_INSTANCE-image:$GITHUB_SHA"
    
    # Add pruning and IP address update to VM startup script
    - name: Update startup script to prune and update IP address
      run: |-
        gcloud compute instances add-metadata $GCE_INSTANCE \
          --zone "$GCE_INSTANCE_ZONE" \
          --metadata=startup-script="#! /bin/bash
            docker image prune -af"
    
    # Deploy the Docker image to GCE
    - name: Deploy
      run: |-
        gcloud compute instances update-container "$GCE_INSTANCE" \
          --zone "$GCE_INSTANCE_ZONE" \
          --container-image "gcr.io/$PROJECT_ID/$GCE_INSTANCE-image:$GITHUB_SHA"
          
    # Purge old images from GCR (not latest)
    - name: Purge GCR images
      run: |-
        gcloud container images list-tags gcr.io/$PROJECT_ID/$GCE_INSTANCE-image \
          --format="get(digest)" --filter="NOT tags=$GITHUB_SHA" | \
          awk -v image_path="gcr.io/$PROJECT_ID/[email protected]" '{print image_path $1}' | \
          xargs -r gcloud container images delete --force-delete-tags --quiet