Search: Test deprecated field in mixed cluster

Update the test for the deprecated `_source_exclude` parameter to run
against 6.6.0+ now that we've backported the deprecation.

Relates to #33475

rest-api-spec/src/main/resources/rest-api-spec/test/get/70_source_filtering.yml

@@ -75,7 +75,7 @@
 "Deprecated _source_include and _source_exclude":
 
   - skip:
-      version: " - 6.99.99"
+      version: " - 6.5.99"
       reason: _source_include and _source_exclude are deprecated from 6.6.0
       features: "warnings"