submodule-helper: fix usage string

The missing space at the end of the line makes the closing square
bracket sticking to the dash in the next line

Found during localisation v2.36.0 round 1

Signed-off-by: Fangyi Zhou <me@fangyi.io>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: fangyi-zhou

builtin/submodule--helper.c

@@ -1895,7 +1895,7 @@ static int module_clone(int argc, const char **argv, const char *prefix)
 	const char *const git_submodule_helper_usage[] = {
 		N_("git submodule--helper clone [--prefix=<path>] [--quiet] "
 		   "[--reference <repository>] [--name <name>] [--depth <depth>] "
-		   "[--single-branch] [--filter <filter-spec>]"
+		   "[--single-branch] [--filter <filter-spec>] "
 		   "--url <url> --path <path>"),
 		NULL
 	};