Merge branch 'sg/t3420-do-not-grep-in-missing-file'

A test checking interactions between git rebase --quit and autostash in t3420-rebase-autostash.sh has been corrected to use test_path_is_missing instead of ! grep on a file that shouldn't exist in the conflicted state. * sg/t3420-do-not-grep-in-missing-file: t3420-rebase-autostash: don't try to grep non-existing files