Add skip for missing types REST test

This commit adds a skip for the missing types REST test. There was a bug
for an unclosed XContent object on version prior to version 5.0.3 which
is going to lead to different responses on vresions prior to 5.0.3 and
versions on or after version 5.0.3.

rest-api-spec/src/main/resources/rest-api-spec/test/indices.get_mapping/20_missing_type.yaml

@@ -20,6 +20,9 @@
 
 ---
 "Type missing when no types exist":
+  - skip:
+      version: " - 5.0.2"
+      reason: there was a bug prior to 5.0.2
   - do:
       catch: missing
       indices.get_mapping: