Output to stderr when generating stubs is treated as an error

[cursive-ghost]

Sometimes when generating stubs, output to stderr is unavoidable. This should probably not be treated as an error, as long as it seems that the stubs have been generated correctly.

See https://clojurians.slack.com/archives/C0744GXCJ/p1643215485049600 for one example (a warning due to using a newer Clojure version)

See also: https://groups.google.com/d/msgid/cursive/434E384F-C373-41F7-8CE1-AB23FB066C92%40gmail.com - an example where logging sometimes outputs to stderr.