SUMMARY
QImage plugin ignores transparency of 8 bit images with alpha channel.

STEPS TO REPRODUCE
1. Add JXL 8 bit image with transparency to library
2. Open the image with digiKam/showFoto

SOFTWARE/OS VERSIONS
Linux: openSUSE Tumbleweed
KDE Plasma Version: 6.3.4
KDE Frameworks Version: 6.12.0
Qt Version: 6.8.2

ADDITIONAL INFORMATION
From Qt 5.15 documentation: "QColor::QColor(QRgb color) Constructs a color with the value color. The alpha component is ignored and set to solid."

Suggested patch:
```patch
diff --git a/core/dplugins/dimg/qimage/dimgqimageloader_load.cpp b/core/dplugins/dimg/qimage/dimgqimageloader_load.cpp
index 705597d8d..83491f38e 100644
--- a/core/dplugins/dimg/qimage/dimgqimageloader_load.cpp
+++ b/core/dplugins/dimg/qimage/dimgqimageloader_load.cpp
@@ -146,7 +146,7 @@ bool DImgQImageLoader::load(const QString& filePath, DImgLoaderObserver* const o

         for (uint i = 0 ; i < w * h ; ++i)
         {
-            QColor color(*sptr);
+            QColor color = QColor::fromRgba(*sptr);
             dptr[0] = color.blue();
             dptr[1] = color.green();
             dptr[2] = color.red();
```