Fix test on use of external schema jar (#412)

* Fix test on use of external schema jar

One test breaks if path to external schema is set and
test is run from the sqlIntegrationTest task.

core/src/test/java/google/registry/model/transaction/JpaTransactionManagerRuleTest.java

@@ -80,6 +80,7 @@ public class JpaTransactionManagerRuleTest {
 
   @Test
   public void testInitScriptUrl_noOverride() {
+    systemPropertyRule.setProperty(GOLDEN_SCHEMA_RESOURCE_ROOT_PROP, null);
     assertThat(jpaTmRule.getInitScriptUrlOverride()).isEmpty();
   }