Fix a leftover skip (#60932)

Looks like I never updated a test skip many many months ago.

Author: nik9000

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/50_filter.yml

@@ -108,8 +108,8 @@ setup:
 ---
 "Sorting terms":
   - skip:
-      version: " - 7.99.99"
-      reason: fixed in 8.0.0 to be backported to 7.7.0
+      version: " - 7.6.99"
+      reason: fixed in 7.7.0
 
   - do:
       bulk: