[JIT] fix alias assertion (#34268)
Summary:
[This check](https://github.com/eellison/pytorch/blob/019ffdca310d22fdcdc66154fbb79f1b028f24b3/torch/csrc/jit/ir/alias_analysis.cpp#L772) wasn't being triggered for None outputs of tuples, because `mustBeNone` would return false if `num_outputs != 1`. This caused an assertion to fail in alias analysis. It's kind of a convoluted case to repro and I wasn't able to make a succinct one, but I tested internally and it fixed the bug.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34268
Differential Revision: D20261539
Pulled By: eellison
fbshipit-source-id: 95edea10e2971727cfd3f3bc2b6bdf9dbadca6a9
