While on it, fix one oversight in 90fbf7c5, that introduced a reference
to an incorrect value for the compression level of pg_dump.

Author: Justin Pryzby
Reviewed-by: Thomas Munro, Michael Paquier
Discussion: https://postgr.es/m/CA+hUKGJRTLWWPcQfjm_xaOk98M8aROK903X92O0x-4vLJPWrrA@mail.gmail.com