Prevent PullRequestSessionManager.StatusChanged throwing

`PullRequestSessionManager.StatusChanged` was throwing when the repository status changed because it was trying to set `initialized` when the task is already completed. Use `TrySetResult` which doesn't throw when the task has already completed.

Author: grokys

src/GitHub.InlineReviews/Services/PullRequestSessionManager.cs

@@ -236,7 +236,7 @@ async Task StatusChanged()
                 }
 
                 CurrentSession = session;
-                initialized.SetResult(null);
+                initialized.TrySetResult(null);
             }
             catch (Exception e)
             {