chore(deps): update gcr.io/cloud-sql-connectors/cloud-sql-proxy docker tag to v2.15.0 (#519)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

docker-compose.yml

@@ -1,7 +1,7 @@
 services:
   db:
     container_name: cloudsql-proxy
-    image: gcr.io/cloud-sql-connectors/cloud-sql-proxy:2.14.3
+    image: gcr.io/cloud-sql-connectors/cloud-sql-proxy:2.15.0
     restart: unless-stopped
     command: tum-app-422909:europe-west1:tum-app-backend --credentials-file=/secrets/cloudsql/credentials.json --address 0.0.0.0 --port ${DB_PORT:-3306}
     networks: