Fix problem with fibers being cancelled due to timeout and causing fetch deadlock

[jordiolivares]

Hi again, it seems that the process for batching across requests suffers from a deadlock issue.

In particular it can be triggered if the timeout occurs between the time the queue has been popped and the buffer is updated.

To fix this I just wrapped it in an F.uncancelable to fix the deadlock, safely updating the reference before cancellation is finished

[jordiolivares]

Seems like the check is failing only due to the GithubExample test having bad credentials, as per the test error:

java.lang.Exception: Couldn't complete request, returned status: 401 Unauthorized: Body:
[info] {"message":"Bad credentials","documentation_url":"https://docs.github.com/rest"}

[juanpedromoreno]

Thanks again @jordiolivares !