After performing a round trip on a connection, the connection is
usually returned to the idle connection pool. If the write of the
request did not complete successfully, the connection is not
returned.
It is possible for the response to be read before the write
goroutine has finished signalling that its write has completed.
To allow for this, the check to see if the write completed successfully
waits for 50ms for the write goroutine to report the result of the
write.
See comments in persistConn.wroteRequest for more details.
On a slow builder, it is possible for the write goroutine to take
longer than 50ms to report the status of its write, leading to test
flakiness when successive requests unexpectedly use different connections.
Set the timeout for waiting for the writer to an effectively
infinite duration in tests.