community/plasma-mobile: Add lockscreen fix patch
This adds an emergency fix for the lockscreen crashing due to a race condition in the powerdevil screen brightness plugin.
This fix is taken from the Plasma/6.2 branch, and will be in Plasma 6.2.1: https://invent.kde.org/plasma/plasma-mobile/-/commit/9dceef84324391947e6d441eca04fa5072bc9ffa