gitattribute: Mark generated files (GH-7619)


Marked files are collapsed by default in Github pull request.
https://github.com/github/linguistGH-generated-code
(cherry picked from commit c1897eda3d47b182977459a1e9fed4b3854a10a0)

Co-authored-by: INADA Naoki <methane@users.noreply.github.com>
1 file changed