Update docker/build-push-action action to v7

Author: renovate[bot]

.github/workflows/docker-image.yml

@@ -25,7 +25,7 @@ jobs:
 
       - name: Build and push image
         id: docker_build
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           push: true
           tags: ghcr.io/itcr-uni-luebeck/obds2openehr:latest