QProgressDialog's QProgressBar might not update if setLabelText() is called too frequently on macOS

On macOS, when QProgressDialog's setLabelText() method is called too frequently, the progress bar might not update at all (until the dialog loses or regains focus).

Tested on a VirtualBox installation of macOS Big Sur 11.5.1, with latest Xcode and Qt 5.15.2. The same bug is present on macOS 10.15.
The example tries to update the dialog every 1ms. The one without setLabelText() calls work properly, while the one with them updates only the label but not the bar.

The modality of the dialog does not affect the issue. I didn't bother to implement the cancel button for the example

The same example works fine on Windows (and Ubuntu iirc).