RDAP: Mark RdapDomainSearchActionTest as medium

Some tests of RdapDomainSearchAction can take longer, because they create many domains.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=133591753

javatests/google/registry/rdap/BUILD

@@ -36,6 +36,7 @@ java_library(
 
 GenTestRules(
     name = "GeneratedTestRules",
+    medium_tests = ["RdapDomainSearchActionTest"],
     test_files = glob(["*Test.java"]),
     deps = [":rdap"],
 )