Fix Woodpecker CI config to properly handle Docker credentials

.woodpecker.yml

@@ -1,14 +1,13 @@
 steps:
   - name: build
     image: woodpeckerci/plugin-docker-buildx
-    environment:
-      DOCKER_USERNAME:
-        from_secret: docker_username
-      DOCKER_PASSWORD:
-        from_secret: docker_password
     settings:
       repo: registry.example.com/ploughshares
       registry: registry.example.com
+      username:
+        from_secret: docker_username
+      password:
+        from_secret: docker_password
       tags: 
         - latest
         - "${CI_COMMIT_TAG##v}"