rake errors:fetch_log errors when layout is not multiline_request_pattern
$STDERR should be $stderr
Fixes #31884 - Correctly warn about wrong logging layout
When running `rake errors:fetch_log`, if the logging layout isn't set to
`multiline_request_pattern` the task errors out because `$STDERR` doesn't
exist. This is a typo, it should have been `$stderr`, but since we use
stdout for all other messages this has been dropped to be consistant.