Fix #49921 by making the dgspec inner build silent (#49927)

Author: baronfel

src/Cli/dotnet/Commands/Package/Add/PackageAddCommand.cs

@@ -89,7 +89,10 @@ private static void GetProjectDependencyGraph(string projectFilePath, string dgF
             $"-property:RestoreDotnetCliToolReferences=false",
 
             // Output should not include MSBuild version header
-            "-nologo"
+            "-nologo",
+
+            // Set verbosity to quiet to avoid cluttering the output for this 'inner' build
+            "-v:quiet"
         ];
 
         var result = new MSBuildForwardingApp(args).Execute();