[OpenMPOpt][FIX] Properly track changes to NestedParallelism

If we update the state, or indicate a pessimistic fixpoint, we need to
consider NestedParallelism too.

Fixes part of https://github.com/llvm/llvm-project/issues/66708

That said, the reproducer still needs malloc which we don't support on
AMD GPU. Will be added later.