dont test squelched warnings against the filter
dont test squelched warnings against the filter

I spent days on Ibcf09af25228d39ee5a943fda82d8a9302433726
reading it over and over again and noticed this slight inaccuracy
10 seconds after I merged it.

the assert_warns_message() and assert_warns() functions should
not consider a mismatched warning class as valid for a match.

Change-Id: Ib8944dd95bcec1a7e4963917a5f4829e2ba27732

sqlalchemy/sqlalchemy,zzzeek/sqlalchemy