[ng] tests: fix spurious failure due to non-POSIX shells

Seen on, e.g., Solaris 10.

* t/internals.tap: Here, by making sure a POSIX shell is used to
run the recipe in the Makefiles running our unit tests.

Signed-off-by: Stefano Lattarini <stefano.lattarini@gmail.com>
1 file changed