Cancellation token is not fired when Event Hubs processor loses lease

[paulbatum]

A customer is reporting that they are seeing significant amounts of duplicate events in their event hubs processing workload. These duplicates are due to loss of partition lease, but when this happens, the cancellation token passed into the function execution should be triggered. The customer is checking the state of that token but they never see it cancelled.

We made a fix a while back, where we found that the cancellation token was not passed through correctly, see here:
#1626

But despite that fix, the token continues to not be triggered. We need to figure out why.