fixup! checkout-index: add --sparse option

Needed to maintain existing behavior for stash. This should not cause a major
performance hit, since the index being checked-out contains only the untracked
files stashed with a prior `git stash -u`.

Signed-off-by: Victoria Dye <[email protected]>

Author: vdye

builtin/stash.c

@@ -350,7 +350,7 @@ static int restore_untracked(struct object_id *u_tree)
 
 	child_process_init(&cp);
 	cp.git_cmd = 1;
-	strvec_pushl(&cp.args, "checkout-index", "--all", NULL);
+	strvec_pushl(&cp.args, "checkout-index", "--all", "--sparse", NULL);
 	strvec_pushf(&cp.env_array, "GIT_INDEX_FILE=%s",
 		     stash_index_path.buf);