t9146: use 'svn_cmd' wrapper

Using 'svn' directly may not work for all users.

Signed-off-by: Eric Wong <normalperson@yhbt.net>

Author: Eric Wong

t/t9146-git-svn-empty-dirs.sh

@@ -122,7 +122,7 @@ test_expect_success 'git svn gc-ed files work' '
 		: Compress::Zlib may not be available &&
 		if test -f "$unhandled".gz
 		then
-			svn mkdir -m gz "$svnrepo"/gz &&
+			svn_cmd mkdir -m gz "$svnrepo"/gz &&
 			git reset --hard $(git rev-list HEAD | tail -1) &&
 			git svn rebase &&
 			test -f "$unhandled".gz &&