t1308: do not get fooled by symbolic links to the source tree

When your $PWD does not match $(/bin/pwd), e.g. you have your copy of the git source tree in one place, point it with a symbolic link, and then "cd" to that symbolic link before running 'make test', one of the tests in t1308 expects that the per-user configuration was reported to have been read from the true path (i.e. relative to the target of such a symbolic link), but the test-config program reports a path relative to $PWD (i.e. the symbolic link). Instead, expect a path relative to $HOME (aka $TRASH_DIRECTORY), as per-user configuration is read from $HOME/.gitconfig and the test framework sets these shell variables up in such a way to avoid this problem. Signed-off-by: Junio C Hamano <gitster@pobox.com>