UniqueViolation: duplicate key value violates unique constraint "origin_visit_pkey"

https://sentry.softwareheritage.org/organizations/swh/issues/9545/?referrer=phabricator_plugin

UniqueViolation: duplicate key value violates unique constraint "origin_visit_pkey"
DETAIL:  Key (origin, visit)=(179514690, 2) already exists.
CONTEXT:  SQL function "swh_origin_visit_add" statement 1

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  File "swh/core/api/negotiation.py", line 81, in __call__
    result = self.func(*args, **kwargs)
  File "swh/core/api/__init__.py", line 510, in f
    ret = obj_meth(**kw)
  File "swh/core/db/common.py", line 73, in _meth
    return meth(self, *args, db=db, cur=cur, **kwargs)
  File "swh/storage/postgresql/storage.py", line 1026, in origin_visit_add
    visit.origin, visit.date, visit.type, cur=cur
  File "swh/storage/postgresql/db.py", line 474, in origin_visit_add
    "SELECT swh_origin_visit_add(%s, %s, %s)", (origin, ts, type)

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Migrated from T4444 (view on Phabricator)