Support update on existing branch through create worker version

Sentry Issue: ARKINDEX-BACKEND-1S4

UniqueViolation: duplicate key value violates unique constraint "process_gitref_name_repository_id_69d1693d_uniq"
DETAIL:  Key (name, repository_id)=(master, 7860e9fb-b02f-40c0-91c9-19882700f38b) already exists.

  File "django/db/backends/utils.py", line 89, in _execute
    return self.cursor.execute(sql, params)

IntegrityError: duplicate key value violates unique constraint "process_gitref_name_repository_id_69d1693d_uniq"
DETAIL:  Key (name, repository_id)=(master, 7860e9fb-b02f-40c0-91c9-19882700f38b) already exists.

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  File "arkindex/process/api.py", line 2248, in create
  File "contextlib.py", line 79, in inner
    return func(*args, **kwds)
  File "arkindex/process/serializers/workers.py", line 577, in create