mail/exim: fix queue runners that are not starting

upstream:

• https://bugs.exim.org/show_bug.cgi?id=3046
• https://github.com/Exim/exim/commit/ced0bbf43860a2e4ddc88e3ba20ae731324586c5

PR: 275635
Author: Niels Kobschätzki <niels@kobschaetzki.net>
Approved-by: fluffy (implicit)