Trying to build Discover master, I'm getting a number of errors like:
```
CMake Error: The INTERFACE_QT_MAJOR_VERSION property of "Qt5::Core" does
not agree with the value of QT_MAJOR_VERSION already determined
for "CategoriesTest".

CMake Error: The INTERFACE_QT_MAJOR_VERSION property of "Qt6::Widgets" does
not agree with the value of QT_MAJOR_VERSION already determined
for "plasma-discover".
```

My system packages are all up to date, so what does this mean?