Mark VerifyEntityIntegrityActionTest as a medium test

It was timing out occasionally in the Bazel build on less-powerful hardware.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=132378555

javatests/google/registry/monitoring/whitebox/BUILD

@@ -43,6 +43,7 @@ java_library(
 
 GenTestRules(
     name = "GeneratedTestRules",
+    medium_tests = ["VerifyEntityIntegrityActionTest"],
     test_files = glob(["*Test.java"]),
     deps = [":whitebox"],
 )