Un-Ignore a test in DomainApplicationCreateFlowTest

A little injection-foo makes this test possible to run.

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=154442134

java/google/registry/tmch/TmchXmlSignature.java

@@ -56,7 +56,7 @@ import org.xml.sax.SAXException;
 
 /** Helper class for verifying TMCH certificates and XML signatures. */
 @ThreadSafe
-public final class TmchXmlSignature {
+public class TmchXmlSignature {
 
   @VisibleForTesting
   final TmchCertificateAuthority tmchCertificateAuthority;