Fix rest test skip version
multi_span prefix queries do not work with the prefix field
before 6.4.
Relates
@@ -66,7 +66,7 @@ setup:
---
"search index prefixes with span_multi":
- skip:
- version: " - 6.2.99"
+ version: " - 6.3.99"
reason: span_multi throws an exception with prefix fields on < versions
- do:
