patchsparse-checkout: fix a couple minor memory leaks

> From: Elijah Newren <newren@gmail.com>
> 
> These were introduced in commit 55dfcf9591 ("sparse-checkout: clear
> tracked sparse dirs", 2021-09-08) and missed in my review at the time.
> Plug the leaks.
> 
> Signed-off-by: Elijah Newren <newren@gmail.com>
> ---
>     sparse-checkout: fix a couple minor memory leaks
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-git-1189%2Fnewren%2Fsparse-directory-cleaning-memleaks-v1
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-git-1189/newren/sparse-directory-cleaning-memleaks-v1
> Pull-Request: https://github.com/git/git/pull/1189
> 
>  builtin/sparse-checkout.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/builtin/sparse-checkout.c b/builtin/sparse-checkout.c
> index 679c1070368..c655517e019 100644
> --- a/builtin/sparse-checkout.c
> +++ b/builtin/sparse-checkout.c
> @@ -185,6 +185,8 @@ static void clean_tracked_sparse_directories(struct repository *r)
>  				item->string);
>  		}
>  
> +		strvec_clear(&s);
> +		clear_pathspec(&p);
>  		dir_clear(&dir);
>  	}