The yielding code currently trips an invariant if a yield is attempted inside a WriteUnitOfWork. We could consider relaxing this to silently skip the yield in non-debug builds, and replacing it with a debug-only fatal assertion in debug builds.

The reason for making this change would be to prevent the invariant from getting tripped in the wild (which would turn the correctness issue of crashing into the performance issue of not yielding). Reasons not to make this change would be to help catch such bugs earlier in development.