qt: Choose monospaced font in C++ code rather in `*.ui` file Setting the "Monospace" font family in a `*.ui` file does not work on macOS, at least on Big Sur with Qt 5.15 (neither via the "font" property nor via the "styleSheet" property). Qt chooses the ".AppleSystemUIFont" instead of ".AppleSystemUIFontMonospaced". This change makes macOS choose the correct monospaced font.
