Make DownloadServiceAccountCredentialAction only accept internal auth

This temporarily disables the ability to download service account credentials. We'd like this to go in to next week's release so that we do not expose this functionality to users who otherwise do not have the ability to download the service account credential, while we research on a more secure solution.

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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=223397754

java/google/registry/tools/server/DownloadServiceAccountCredentialAction.java

@@ -38,7 +38,7 @@ import javax.inject.Named;
 @Action(
     path = DownloadServiceAccountCredentialAction.PATH,
     method = {GET},
-    auth = Auth.AUTH_INTERNAL_OR_ADMIN)
+    auth = Auth.AUTH_INTERNAL_ONLY)
 public class DownloadServiceAccountCredentialAction implements Runnable {
 
   private static final FluentLogger logger = FluentLogger.forEnclosingClass();