sparse-index: update command for expand/collapse test
In anticipation of `git reset --hard` being able to use the sparse index
without expanding it, replace the command in `sparse-index is expanded and
converted back` with `git reset -- folder1/a`. This command will need to
expand the index to work properly, even after integrating the rest of
`reset` with sparse index.
Helped-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>