Fix memory leak in Qt event loop integration (#14240) (#14251)
The QEventLoop object, `event_loop`, created in
`IPython/terminal/pt_intputhooks/qt.py` L58 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.
The issue was originally reported by @pag who also suggested the fix.
`pytest IPython/terminal/tests/` runs through without errors. I have
tested the changes and see no more accumulation of `QEventLoop` objects.
This fixes #14240
Matthias Bussonnier