ci: Add load:true to docker build step

Fix Docker image not being available for testing by explicitly
loading the built image into Docker daemon. Required when using
docker/build-push-action with push:false.

Author: libraz

.github/workflows/ci.yml

@@ -142,6 +142,7 @@ jobs:
         context: .
         file: ./Dockerfile
         push: false
+        load: true
         tags: mygramdb:test
         cache-from: type=gha
         cache-to: type=gha,mode=max