Uppercased file extensions in macro ui elements causing crashes
I found that Excel macros containing UI elements with uppercased file extensions will cause an error in openpyxl/packaging/manifest.py on line 193 because the map has all the extensions lowercased so looking up an uppercased extension finds nothing.
To fix this I changed
mime = mimetypes.types_map[True][ext]
tomime = mimetypes.types_map[True][ext.lower()]
This cleared up the issue for me so I figured this might be helpful for someone else.
I considered doing a MR for this but the change is just so very small it didn't seem worth it.