Update InvalidScopeMessage allowed characters list (Azure#33027)

Co-authored-by: Anton Kolesnyk <[email protected]>

Author: antkmsft

sdk/identity/Azure.Identity/src/ScopeUtilities.cs

@@ -15,7 +15,7 @@ internal static class ScopeUtilities
         private const string DefaultSuffix = "/.default";
         private const string ScopePattern = "^[0-9a-zA-Z-_.:/]+$";
 
-        private const string InvalidScopeMessage = "The specified scope is not in expected format. Only alphanumeric characters, '.', '-', ':', and '/' are allowed";
+        private const string InvalidScopeMessage = "The specified scope is not in expected format. Only alphanumeric characters, '.', '-', ':', '_', and '/' are allowed";
         private static readonly Regex scopeRegex = new Regex(ScopePattern);
 
         public static string ScopesToResource(string[] scopes)