11479 Private Tags Bug (rebased onto develop)



This is the same as gh-2369 but rebased onto develop.

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@will-moore, this test currently fails but not because the tag is (or is not) readable but because the changing the permissions on the group is not possible. I'll need help reproducing the issue, or perhaps it's been fixed.

@ximenesuk, python job will be read until this is dealt with.