Fix directory permissions in import_to_synapse (#584)

* Fix directory permissions in import_to_synapse

The directory permissions 0655 map to rw-r-x-rx, which excludes the owner
from accessing created directories, which the creation of directories in
the media store.

* changelog

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Co-authored-by: Martin Weinelt <hexa@helix.lossy.network>
Co-authored-by: Travis Ralston <travis@t2bot.io>