Demonstrate possible regression

I noticed that a possible regression was introduced with this change: https://github.com/immerjs/immer/commit/452a5085c0f84c3277ee16ab9b072ad99127ce90#diff-4ade25325a6cd7d1cca619364c84d19bfa47e6939a2c1b38d065767255b8f86eL68

The error is:

TypeError: Cannot perform 'get' on a proxy that has been revoked

If you try this unit test on the commit before, it passes.

I don’t have enough context to know what the correct fix should be or whether this is working as intended, but I thought I’d at least demonstrate a failing unit test case.