Update the create_pool function in the client.py file of the psycopg backend to eliminate the runtime warning of psycopg_pool

[zxj17815]

Description

psycopg_pool updated and generated a RuntimeWarning.

RuntimeWarning: opening the async pool AsyncConnectionPool in the constructor is deprecated and will not be supported anymore in a future release. Please use `await pool.open()`, or use the pool as context manager using: `async with AsyncConnectionPool(...) as pool: `..."

This update is change "create_pool" function, call "await pool.open()" explicitly.

Motivation and Context

There is a warning when using it. After checking the official documentation, I found that the official update has a RuntimeWarning.

How Has This Been Tested?

Use pgsql and the driver uses the latest psycopg and psycopg_pool

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added the changelog accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

[coveralls]

Pull Request Test Coverage Report for Build 10384410457

Details

• 3 of 3 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.002%) to 89.092%

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Totals
Change from base Build 10244831838:	0.002%
Covered Lines:	5962
Relevant Lines:	6577

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💛 - Coveralls