Update renderer on SwitchSelectionEndpoint (#13435)

## Summary of the Pull Request
In #13370, we should be notifying the renderer that the selection changed. Minor oversight and simple fix.

## References
#4993
#13370
Closes #13413

(cherry picked from commit 66ecb0b)
Service-Card-Id: 83892665
Service-Version: 1.15

src/cascadia/TerminalControl/ControlCore.cpp

@@ -1094,6 +1094,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
         if (_terminal->IsSelectionActive())
         {
             _terminal->SwitchSelectionEndpoint();
+            _updateSelectionUI();
             return true;
         }
         return false;