fix(pgvector): fix vector extension not existing before register_vector

[s-h-a-d-o-w]

This fixes:

Traceback (most recent call last):
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/vectordb_bench/interface.py", line 179, in _async_task_v2
    case_res.metrics = runner.run(drop_old)
                       ^^^^^^^^^^^^^^^^^^^^
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/vectordb_bench/backend/task_runner.py", line 151, in run
    self._pre_run(drop_old)
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/vectordb_bench/backend/task_runner.py", line 142, in _pre_run
    self.init_db(drop_old)
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/vectordb_bench/backend/task_runner.py", line 131, in init_db
    self.db = db_cls(
              ^^^^^^^
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/vectordb_bench/backend/clients/pgvector/pgvector.py", line 58, in __init__
    self.conn, self.cursor = self._create_connection(**self.connect_config)
                             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/vectordb_bench/backend/clients/pgvector/pgvector.py", line 93, in _create_connection
    register_vector(conn)
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/pgvector/psycopg/register.py", line 12, in register_vector
    register_vector_info(context, info)
  File "/home/andy/temp/vdbb/.venv/lib/python3.12/site-packages/pgvector/psycopg/vector.py", line 49, in register_vector_info
    raise psycopg.ProgrammingError('vector type not found in the database')
psycopg.ProgrammingError: vector type not found in the database

[sre-ci-robot]

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