It's impossible to tell why #50754 fails without this change.
We're failing to close the `exchange` somewhere and there is no
write timeout in the GCS SDK (something to look into separately)
only a read timeout on the socket so if we're failing on an assertion without
reading the full request body (at least into the read-buffer) we're locking up
waiting forever on `write0`.
This change ensure the `exchange` is closed in the tests where we could lock up
on a write and logs the failure so we can find out what broke #50754.
4a7e09f624