GitHub creates padding for a screenshot used in metainfo file

Hi all. I’m trying to include an screenshot to the metainfo file for an application, but appstream-util fails the metainfo validation with the following errors: <image> has vertical padding and <image> has horizontal padding. I haven’t added any padding, and I don’t see padding when I download the image from GitHub, so what could be causing this? The image in question is below:
With padding
Without padding

That shouldn’t be an issue.

but appstream-util fails the metainfo validation

appstream-util is deprecated. Please run validation with the linter MetaInfo guidelines | Flathub Documentation