for CORE::my $var (...) {} is legal syntax, hence test it

for CORE::my $var (...) {} is legal syntax, hence test it

We had tests for CORE::state, but not CORE::my or CORE::our. It happens that
they are all legal syntax, but seemingly more be accident than design. They
are only accepted by yyl_foreach() as a quirk of the current implementation.

Note that for my Dog $spot (...) {} is legal, but not CORE::my. our Dog is
legal, CORE::our is not. Neither state Dog nor CORE::state are legal. These
are all emergent behaviour of the parser - do not take these tests as
"correct", merely as verifying that current behaviour doesn't change unless
we intended it to.