Fix memory leak in Qt event loop integration (#14240)

See: https://github.com/ipython/ipython/issues/14240

- the QEventLoop, `event_loop`, is not deleted when exiting the scope as
passing `app` to the constructor parents the object to `app`. This
creates a memory leak as QEventLoop objects are being accumulated.
- issue reported by and fix suggested by @pag

IPython/terminal/pt_inputhooks/qt.py

@@ -84,3 +84,5 b' def inputhook(context):'
                 _exec(event_loop)
         finally:
             notifier.setEnabled(False)
+    # make sure that the QObject is being deleted
+    event_loop.setParent(None)