ci(docker-build): fix `when`

.woodpecker/docker-build.yml

@@ -1,7 +1,6 @@
 variables:
   - &buildx woodpeckerci/plugin-docker-buildx:2.0.0
   - &platforms linux/amd64
-  - &when_path ".woodpecker/docker-build.yml"
 
 matrix:
   DOCKERFILE:
@@ -19,7 +18,7 @@ pipeline:
     when:
       event: pull_request
       path:
-        - *when_path
+        - .woodpecker/docker-build.yml
         - .woodpecker/docker/${DOCKERFILE}
 
   publish:
@@ -37,7 +36,7 @@ pipeline:
     when:
       event: push
       path:
-        - *when_path
+        - .woodpecker/docker-build.yml
         - .woodpecker/docker/${DOCKERFILE}
 
 branches: master