Test: Fix filter assertion

Forces a test to use only a single shard so the assertion about the
aggregation profiler results are correct. Without this the test fails
randomly but very rarely. We have to use multiple shards (seeded random
10% choice) and we have to land all of the documents on one shard
(unseeded random 3.2%) and that shard has to be the second shard in the
list (unseeded random 50%). That works out to about 1.6% chance with an
appropriate seed - .16% without it.

Author: nik9000

rest-api-spec/src/main/resources/rest-api-spec/test/search.aggregation/370_doc_count_field.yml

@@ -151,6 +151,7 @@ setup:
 "Test filters agg with doc_count":
   - skip:
       version: " - 7.11.1"
+      features: default_shards
       reason: "fixed in 7.11.2"
   - do:
       search: