Check for debug suite for upload suite, not override suite

Debug packages are exempt from NEW if the target suite has a seperate
debug suite.  However the code checked if the target's override suite
had a debug suite...  For the Debian archive this went unnoticed as
experimental's override suite is unstable and both suites have a
seperate debug suite.

Reported-by: Matthias Klumpp <mak@debian.org>