[A11y][Fastpass] Add role attribute where aria-label attribute is used (#9349)

* add role attribute

* add informational comment

Author: keylime-unicorn

src/NuGetGallery/ViewModels/ThirdPartyPackageManagerViewModel.cs

@@ -19,7 +19,8 @@ public ThirdPartyPackageManagerViewModel(string name, string contactUrl) : base(
         {
             ContactUrl = contactUrl;
             AlertLevel = AlertLevel.Warning;
-            AlertMessage = "<b display=\"none\" aria-label=\"warning\"></b> The NuGet Team does not provide support for this client. Please contact its "
+            // the b tag below adds an element that is not displayed, but that allows screen readers to announce "warning" before the following alert message text
+            AlertMessage = "<b display=\"none\" aria-label=\"warning\" role=\"alert\"></b> The NuGet Team does not provide support for this client. Please contact its "
                 + $"<a href=\"{contactUrl}\" aria-label=\"Contact the maintainers of the {name} client\">maintainers</a> for support.";
         }
     }