t2402: test worktree path when called in .git directory

t2402: test worktree path when called in .git directory

The bug which reports an extra `/.git/.` in worktree path when called in
'.git' directory already has been fixed. But unfortunately, the regression
test to ensure this behavior has been forgotten.
Here is that test.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Hariom Verma <hariom18599@gmail.com>
Acked-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>