fix: Update main image name for proxy deployment in workflow

Author: FelixTJDietrich

.github/workflows/deploy.yml

@@ -34,7 +34,7 @@ jobs:
       environment: "Production"
       docker-compose-file: "./docker/compose.proxy.yaml"
       # We just keep the main-image-name and image-tag as placeholders
-      main-image-name: ls1intum/proposal-review-assistant
+      main-image-name: ls1intum/proposal-review-assistant/app
       image-tag: ${{ inputs.image-tag }}
       deployment-base-path: "/opt/proxy"
     secrets: inherit