t/t7407: fix two typos in submodule tests

In t/t7407-submodule-foreach.sh there is a typo in one of the
path names given for a test step.  The correct path is
nested1/nested2/.git, but nested1/nested1/nested2/.git is
given instead.  The typo is hidden because this line also
accidentally omits the && chain operator.  The omitted chain
also means the return values of all the previous commands in
this test are also being ignored.

Fix the path and add the chain operator so the entire test
sequence can be properly validated.

Signed-off-by: Phil Hord <hordp@cisco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>