Follow-up to Ben's PR #37892. Adds a TestInternalCredential block to
test_dashboard_auth_ws_tickets.py exercising the mint-once stability,
multi-use, unminted-rejection, empty-value, wrong-value, reset-and-remint,
and ticket-store-independence branches directly (previously only covered
indirectly via _ws_auth_ok, which left the unminted and empty-value
branches unexercised).
Also corrects the consume_internal_credential docstring: the returned
identity dict is discarded by the current _ws_auth_ok caller (which only
needs the boolean outcome), so the prior 'carry it into its session log'
wording over-promised.
e114b31eda