t1301: fix wrong template dir for git-init
The template dir prepared in test case "forced modes" is not used as
expected because a wrong template dir is provided to "git init". This is
because the $CWD for "git-init" command is a sibling directory alongside
the template directory. Change it to the right template directory and
add a protection test using "test_path_is_file".
The wrong template directory was introduced by mistake in commit
e1df7fe43f (init: make --template path relative to $CWD, 2019-05-10).
Signed-off-by: Jiang Xin <zhiyou.jx@alibaba-inc.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>