Fix a bug in the BWC tests where we added a field alias in unsupported versions.

Author: jtibshirani

rest-api-spec/src/main/resources/rest-api-spec/test/search/110_field_collapsing.yml

@@ -7,7 +7,6 @@ setup:
             test:
               properties:
                 numeric_group: { type: integer }
-#                group_alias: { type: alias, path: numeric_group }
 
   - do:
       index:
@@ -398,8 +397,16 @@ setup:
 ---
 "field collapsing on a field alias":
   - skip:
-      version: " - 6.9.99"
-      reason: Field aliases require non-BWC index setup / Field aliases were introduced in 6.4.0.
+      version: " - 6.3.99"
+      reason: Field aliases were introduced in 6.4.0.
+  - do:
+      indices.put_mapping:
+        index: test
+        type: test
+        body:
+          test:
+            properties:
+              group_alias: { type: alias, path: numeric_group }
   - do:
       search:
         index: test