cli.admin: Add remaining coverage on `swh deposit reschedule` cli

This adds the remaining missing coverage on the swh deposit reschedule cli. This also clarifies the messages in the runtime code, this serves multiple purposes:

• 1. message were not always clear
• 2. allows to use f-string which clarifies technically the code
• 3. ultimately, the coverage is then shown by jenkins in this very diff...

This cli allows to reschedule deposit ingestions which failed or got missed for some reason.

Test Plan

tox

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Migrated from D4256 (view on Phabricator)