Bug 33360: (follow-up) Adjust wording in verbose mode

Bug 33360: (follow-up) Adjust wording in verbose mode

Koha reports 'sending mail' while we actually are still
processing mail. It could still be delayed, fail, etc.

Test plan:
Run process_message_queue in verbose mode. If a message
get processed, you should see:
    Processing email message to patron: 51 at /usr/share/koha/C4/Letters.pm line 1008.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>