lint-python.sh is broken, at least on my machine

[kristapsk]

By #1484.

We didn't notice, because CI calls flake8 directly, instead of ./test/lint/lint-python.sh. Another thing to fix.

src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QDate' imported but unused
src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QDateTime' imported but unused
src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QObject' imported but unused
src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QPoint' imported but unused
src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QRect' imported but unused
src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QTime' imported but unused
src/jmqtui/open_wallet_dialog.py:11:1: F401 'PySide2.QtCore.QUrl' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QConicalGradient' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QCursor' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QFontDatabase' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QIcon' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QKeySequence' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QLinearGradient' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QPainter' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QPixmap' imported but unused
src/jmqtui/open_wallet_dialog.py:13:1: F401 'PySide2.QtGui.QRadialGradient' imported but unused
16    F401 'PySide2.QtCore.QDate' imported but unused
^---- failure generated from ./test/lint/lint-python.sh

I remember that there were some special handling for this before, because that file is auto-generated from Qt Designer.