try docker @ ci.

.drone.yml

@@ -1,7 +1,6 @@
 kind: pipeline
 type: docker
 name: default
-
 steps:
   - name: test
     image: maven:3.8-openjdk-18-slim
@@ -26,3 +25,9 @@ steps:
       event:
         exclude:
           - pull_request
+  - name: build_docker_image
+    plugin: docker
+    commands: docker image build -f docker/Dockerfile .
+    when:
+      branch:
+        - feature/docker