Exchange nightly not fully working bell update check with the daily/reliable method

Closes #635 (closed)

What does this MR do?

Exchange nightly not fully working bell update check which didn't delete expired bells with the daily/reliable method.

How confident are you it won't break things if deployed?

92%

Links to related issues

None?

How to test

Steps a reviewer can take to verify that this MR does what it says it does e.g.

1. Checkout branch locally
2. Login as store manager
3. Create a slot at a specific $time which is very soon
4. Logout as store manager
5. Login as a foodsaver of this store
6. Join this slot before $time passed
7. Wait until $time passed
8. Logout as foodsaver
9. Login as store manager
10. See there are "1 unapproved foodsavers"
11. Execute nightly run: ./scripts/docker-compose run --rm --no-deps app php -f run.php Maintenance daily
12. Refresh page
13. See there is NO entry like "0 unapproved foodsavers" (this also works at a test during daytime, as all unapproved slots are deleted with a pre existing script with this command)

Screenshots

None - backend change.. Well kind of with the previous 0 bell entry:

Checklist

• added a test, or explain why one is not needed/possible...
• no unrelated changes
• asked someone for a code review
• joined #foodsharing-beta channel at https://slackin.yunity.org
• added an entry to CHANGELOG.md (description, merge request link, username(s))
• Once your MR has been merged, you are responsible to update the #foodsharing-beta Slack channel about what has been changed here. They will test your work in different browsers, roles or other settings