[LyX/master] Fix Qt6 deprecation warning (QString::fromUcs4(uint))

[Enrico Forestieri]

On Sun, Mar 21, 2021 at 05:00:32PM +0100, Jürgen Spitzmüller wrote:
> Am Sonntag, dem 21.03.2021 um 16:56 +0100 schrieb Enrico Forestieri:
> > On Windows it doesn't even compile
> 
> Reverted.

Fixed properly at 6fa973b3.

-- 
Enrico