phase-shelve: correct unicode string to honor 'shelve.store=internal'
Follow-up to !198 (merged), this MR corrects str to bytes and adds a test capturing the failure it caused.
This instance will be upgraded to Heptapod 1.3.1 (GitLab 16.9.3) on 2023-03-28 at 17:00 UTC+1
Follow-up to !198 (merged), this MR corrects str to bytes and adds a test capturing the failure it caused.