Increase the number of RDAP test shards

The RDAP tests (particularly domain search) take the longest out of anything in our test suite, so bump up the shard count to make it go faster.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202018020

javatests/google/registry/rdap/BUILD

@@ -40,7 +40,7 @@ java_library(
 GenTestRules(
     name = "GeneratedTestRules",
     medium_tests = ["RdapDomainSearchActionTest"],
-    shard_count = 4,
+    shard_count = 6,
     test_files = glob(["*Test.java"]),
     deps = [":rdap"],
 )