[mlgo][aot] requrie the model is autogenerated for test determinism

The tests that exercise the 'release' mode, where the model is AOT-ed,
check the output has certain properties, to validate that, indeed, a
different policy from the default one was exercised. For determinism, we
can't reliably check that output for an arbitrary learned policy, since
it could be that policy happens to mimic the default one in that
particular case.

This patch adds a requirement that those tests run only when the model
is autogenerated (e.g. on build bots).

Differential Revision: https://reviews.llvm.org/D111747