How to reference the image specified by imageToDeploy in my YAML?

The docs mention this:

> Image and application source arguments (e.g., appSourcePath, imageToDeploy) will still be used to first build and/or push an image that is used by the Container App; in this case, the provided YAML configuration file will need to reference the image specified by imageToDeploy (or imageToBuild, depending on your scenario).

This is my actuin:

```yaml
- name: Build and push container image to registry
uses: azure/container-apps-deploy-action@v2
with:
appSourcePath: ${{ github.workspace }}
dockerfilePath: App1-Web/Dockerfile
registryUrl: app1.azurecr.io
registryUsername: ${{ secrets.REGISTRY_USERNAME }}
registryPassword: ${{ secrets.REGISTRY_PASSWORD }}
containerAppName: app-1-web
resourceGroup: App1-ACA-RG
imageToBuild: app1.azurecr.io/app-1-web:${{ github.sha }}
```

Notice ${{ github.sha }} is my tag. How do I use GitHub Actions Variables in the config YAML?