Fix access to dotted field from source in yaml test

Author: eyalkoren

modules/ingest-common/src/yamlRestTest/resources/rest-api-spec/test/ingest/210_conditional_processor.yml

@@ -107,6 +107,6 @@ teardown:
         index: test
         id: "1"
   - match: { _source.bytes_source_field: "1kb" }
+  - match: { _source.conditional\.field: "bar" }
   - match: { _source.bytes_target_field: 1024 }
 
-