tests/qtest: Run the PPC 32-bit tests with the 64-bit target binary, too

The ppc64 target is a superset of the 32-bit target, so we should
include the tests here, too. This used to be done in the past already,
but it got lost during the conversion to meson.

Fixes: a2ce7dbd ("meson: convert tests/qtest to meson")
Message-Id: <20211201104347.51922-2-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>