[BUG] git clone gives error on macOS (filename case insensitivity)

### Version of Kakoune master ### Reproducer The macOS filesystem is case insensitive. Filenames that collide in a case insensitive filesystem should not be checked into kakoune. ```bash $ git clone https://github.com/mawww/kakoune.git Cloning into 'kakoune'... remote: Enumerating objects: 60018, done. remote: Counting objects: 100% (1816/1816), done. remote: Compressing objects: 100% (735/735), done. remote: Total 60018 (delta 1341), reused 1115 (delta 1063), pack-reused 58202 (from 3 Receiving objects: 100% (60018/60018), 42.74 MiB | 11.77 MiB/s, done. Resolving deltas: 100% (41828/41828), done. warning: the following paths have collided (e.g. case-sensitive paths on a case-insensitive filesystem) and only one from the same colliding group is in the working tree: 'test/normal/object/nested/around/WORD/cmd' 'test/normal/object/nested/around/word/cmd' 'test/normal/object/nested/around/WORD/in' 'test/normal/object/nested/around/word/in' 'test/normal/object/nested/around/WORD/kak_quoted_selections' 'test/normal/object/nested/around/word/kak_quoted_selections' 'test/normal/object/nested/inner/WORD/cmd' 'test/normal/object/nested/inner/word/cmd' 'test/normal/object/nested/inner/WORD/in' 'test/normal/object/nested/inner/word/in' 'test/normal/object/nested/inner/WORD/kak_quoted_selections' 'test/normal/object/nested/inner/word/kak_quoted_selections' ``` ### Outcome git complains ### Expectations git should not complain ### Additional information _No response_