Test `QMenu.addAction` with a shortcut of `Qt.Key` type as well. The argument type causes the following error on `PySide2`:
```plaintext
TypeError: 'PySide2.QtWidgets.QAction.setShortcut' called with wrong argument types:
  PySide2.QtWidgets.QAction.setShortcut(Key)
Supported signatures:
  PySide2.QtWidgets.QAction.setShortcut(PySide2.QtGui.QKeySequence)
```

Fix the omission of `Qt.Key` check.
Fix a crash when `QAction.setShortcuts` gets a single shortcut.
Add tests for the cases.
Refactor a little.

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…d PyQt5

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…d PyQt5

Some 6.3.2 builds still seem to lack the flexibility.

…doba12

…nt as suggested by @ccordoba12

The test is expected to fail on Qt6 >= 6.5.
The earlier versions of PyQt/PySide are patched against the fail, so don't test them.

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