Blacklisted items don't prevent parent directory etags from updating

[ckamm]

Currently if an item is blacklisted it will not be reattempted. Instead it's set to Ignored and BlacklistedError. The intention is that we want to show the sync as successful and silently reattempt the file after some time. (the value of the whole feature is debatable)

The problem with this approach becomes clear in a specific scenario: Say the file A/foo.txt can't be downloaded and gets blacklisted after the first sync. On the second sync it doesn't get attempted and the sync as well as PropagateDirectory for A is successful, updating the etag of A. When the blacklist entry expires the client will know longer be aware that it needs to rediscover A and do something inside it.

[ckamm]

PR #6412

[ckamm]

Keeping this open because I still want to add blacklisting tests - we've had none of them for too long.

[guruz]

This bug must exist since ages?