[unpackfs] Fix schema validation

- the *weight* key was introduced without a corresponding schema
  change, so the examples didn't validate anymore.

src/modules/unpackfs/unpackfs.schema.yaml

@@ -17,4 +17,5 @@ properties:
                 destination: { type: string }
                 excludeFile: { type: string }
                 exclude: { type: array, items: { type: string } }
+                weight: { type: integer, exclusiveMinimum: 0 }
             required: [ source , sourcefs, destination ]