Added per-step when clause

.woodpecker/.test.yml

@@ -1,13 +1,15 @@
+# When block for each step is temporary until top-level when is properly implemented
 pipeline:
   clippy:
     image: 'rust:1.57'
     commands:
       - cargo clippy -- -D clippy::all --no-deps
+  when:
+    event: pull_request
 
   tests:
     image: 'rust:1.57'
     commands:
       - cargo test
-
+  when:
-when:
+    event: pull_request
-  event: pull_request