Revert change of Image surface color type from 24 to 32 bit

In a previous change (5c2611d), the case distinction in creation of an
image's surface depending on using GTK 4 or not has been removed. By
accident, this change replaced the previously used 24 bit color format
(for both cases) with a 32 bit color format.
This change revert that accidental modification.

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT/gtk/org/eclipse/swt/graphics/Image.java

@@ -1260,7 +1260,7 @@ void init(int width, int height) {
 	this.type = SWT.BITMAP;
 
 	/* Create the pixmap */
-	surface = Cairo.cairo_image_surface_create(Cairo.CAIRO_FORMAT_ARGB32, width, height);
+	surface = Cairo.cairo_image_surface_create(Cairo.CAIRO_FORMAT_RGB24, width, height);
 	if (surface == 0) SWT.error(SWT.ERROR_NO_HANDLES);
 	// When we create a blank image we need to set it to 100 in GTK3 as we draw using 100% scale.
 	// Cairo will take care of scaling for us when image needs to be scaled.