fix pipeline schema to support branch as an array in 'when' (#836)

pipeline/schema/.woodpecker/test-when.yml

@@ -6,6 +6,13 @@ pipeline:
     when:
       branch: master
 
+  when-branch-array:
+    image: alpine
+    commands:
+      - echo "test"
+    when:
+      branch: [master, deploy]
+
   when-event:
     image: alpine
     commands:

pipeline/schema/schema.json

@@ -200,7 +200,16 @@
         },
         "branch": {
           "description": "TODO Read more: https://woodpecker-ci.org/docs/usage/pipeline-syntax#branch",
-          "type": "string"
+          "oneOf": [
+            {
+              "type": "array",
+              "items": {
+                "type": "string"
+              },
+              "minLength": 1
+            },
+            { "type": "string" }
+          ]
         },
         "event": {
           "description": "TODO Read more: https://woodpecker-ci.org/docs/usage/pipeline-syntax#event",