fix: use correct argument for setArtifact

Author: diegomarquezp

gapic-generator-java/src/test/java/com/google/api/generator/gapic/composer/grpcrest/goldens/EchoStubSettings.golden

@@ -442,7 +442,7 @@ public class EchoStubSettings extends StubSettings<EchoStubSettings> {
   @Override
   protected LibraryMetadata getLibraryMetadata() {
     return LibraryMetadata.newBuilder()
-        .setArtifactName("googleapis/sdk-platform-java")
+        .setArtifactName("com.google.cloud:gapic-showcase")
         .setRepository("googleapis/sdk-platform-java")
         .build();
   }

gapic-generator-java/src/test/java/com/google/api/generator/test/protoloader/GrpcRestTestProtoLoader.java

@@ -93,7 +93,7 @@ public GapicContext parseShowcaseEcho() {
         .setHelperResourceNames(outputResourceNames)
         .setTransport(getTransport())
         .setRepo(ECHO_SERVICE_REPOSITORY)
-        .setArtifact(ECHO_SERVICE_REPOSITORY)
+        .setArtifact(ECHO_SERVICE_ARTIFACT)
         .build();
   }