fix: add missing pillow_jxl import

This import was accidentally removed in #569. This commit restores the import.

tagstudio/src/qt/widgets/thumb_renderer.py

@@ -12,6 +12,7 @@ from pathlib import Path
 
 import cv2
 import numpy as np
+import pillow_jxl  # noqa: F401
 import rawpy
 import structlog
 from mutagen import MutagenError, flac, id3, mp4