Fix database is locked when performing auto cleanup

[Jojo-1000]

Closes #4631, closes #3635

When a backup with --auto-cleanup detects unknown files, a repair is triggered while the database connection is still open. Because repair creates its own database connection, this causes an error The process cannot access the file because it is being used by another process (even though it is the same process).

Steps to reproduce error:

• Create a backup with some files and enable --auto-cleanup
• Run the backup
• To trigger auto-cleanup (repair):
  On the destination, duplicate a dblock file and change a few digits in the name
• To trigger auto-cleanup (recreate):
  Delete the local database of the backup (using UI works)
• The live log shows Backend verification failed, attempting automatic cleanup

Current behavior:

• error: database is locked database is locked in live log
• Backup fails with error The process cannot access the file because it is being used by another process
• (For recreate): Any subsequent manual repair or recreate calls fail with the same error, until duplicati is restarted

New behavior:

• Auto cleanup deletes the extra files/recreates the database
• Backup succeeds with warning Backend verification failed, attempting automatic cleanup and more warnings about the missing/extra files

[duplicatibot]

This pull request has been mentioned on Duplicati. There might be relevant details there:

https://forum.duplicati.com/t/error-uploading-file/16688/3

[duplicatibot]

This pull request has been mentioned on Duplicati. There might be relevant details there:

https://forum.duplicati.com/t/failed-to-read-local-db-duplicati-blocks-itself-access-to-it/16806/7