[Bug 640962] Make check failure: test_backend_dbi

Can't suppress the perfectly legitimate warning, so make it non-fatal;
that way it won't trigger test_checked_handler after the tdata has
popped off the stack.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23004 57a11ea4-9604-0410-9ed3-97b8803252fd