multimedia/qmmp-qt6: update to 2.1.9 release (+)

Changes since 2.1.8:

• fixed build with PipeWire version less than 0.3.33;
• fixed displaying bitrate in the wavpack plugin;
• disabled Qt 6.7 build warnings (2.1.9 only);
• disabled waveform seekbar for CD tracks in the simple user interface.