[wasm] InstallWorkloadFromArtifacts: correctly handle rtm versions

In case of a version like `8.0.100-rtm.23470.1`, we incorrectly
extracted `-rtm.23470` instead of `-rtm`, which resulted in trying to
install package named `Microsoft.NET.Workload.Emscripten.Current.Manifest-8.0.100-rtm.23470` instead of `Microsoft.NET.Workload.Emscripten.Current.Manifest-8.0.100-rtm`.

src/tasks/WorkloadBuildTasks/InstallWorkloadFromArtifacts.cs

@@ -49,7 +49,7 @@ public partial class InstallWorkloadFromArtifacts : Task
  private string _tempDir = string.Empty;
  private string _nugetCachePath = string.Empty;
 
- [GeneratedRegex(@"^\d+\.\d+\.\d+(-[A-z]*\.*\d*)?")]
+ [GeneratedRegex(@"^\d+\.\d+\.\d+(-rtm|-[A-z]*\.*\d*)?")]
  private static partial Regex bandVersionRegex();
 
  public override bool Execute()