These are an implementation quirk, and passing them to the UI just means
that we put TGO pins on top of the CP, which makes the base menu
unopenable.
In the old UI we avoided this by not drawing anything that was
`for_airbase`, but now that we can zoom in further we're drawing base
defenses.
https://bugreports.qt.io/browse/PYSIDE-1426
For whatever reason this only shows up in packaged builds for us, and
also the recommended workaround of using a member property rather than a
decorated method does not work for us.
Until PySide2 5.15.3 (or later) is released, we need to use a named
signal for every property we expose.
