Update to getattr()

This now a one-liner, compared to 6 lines originally.
And it should be (algorithmically) faster.

src/img2pdf.py

@@ -1832,10 +1832,7 @@ def read_images(
             )
     else:
         logger.debug("PIL format = %s", imgdata.format)
-        try:
-            imgformat = ImageFormat[imgdata.format]
-        except KeyError:
-            imgformat = ImageFormat.other
+        imgformat = getattr(ImageFormat, imgdata.format, ImageFormat.other)
 
     def cleanup():
         if imgdata is not None: