Inject clock for Tmch validity using InjectRule instead of manually

Basically a less patchy version of []

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202138086

javatests/google/registry/tools/UpdateSmdCommandTest.java

@@ -73,8 +73,8 @@ public class UpdateSmdCommandTest extends CommandTestCase<UpdateSmdCommand> {
 
   @Before
   public void init() {
-    // Setting the clock used for SignedMark signature validity.
-    TmchCertificateAuthority.clock = () -> DateTime.parse("2015-01-01TZ");
+    // For SignedMark signature validity
+    inject.setStaticField(TmchCertificateAuthority.class, "clock", clock);
     inject.setStaticField(Ofy.class, "clock", clock);
     createTld("xn--q9jyb4c");
     clock.advanceOneMilli();