Line-endings in the patch need to be CRLF to meet the patched file's content.
* gnu/packages/patches/python-piexif-fix-tests-with-pillow-7.2.patch:
Change line-endings of patched lines.
* gnu/packages/python-xyz.scm (python-piexif): New variable.
* gnu/packages/patches/python-piexif-fix-tests-with-pillow-7.2.patch: New file.
* gnu/packages/python-xyz.scm (dist_patch_DATA): Add it.