[Timeline KIO] Don't announce that we can write

It's read-only, trying to copy raises an "unsupported action" error.

All files in here are linked as local files, so opening a file
will actually redirect to the real location and so editing files
works fine without the worker being marked as writable.
3 jobs for !80 with work/kbroulik/unwritable-timeline in 4 minutes (queued for 10 seconds)
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