Changed type annotation in order to have the correct type annotation in

from tortoise.transactions import in_transaction

async def main():
    async with in_transaction() as conn: # <--- here

Description

Changed return type from generic T_conn to TransactionalDBClient

Motivation and Context

#2174

How Has This Been Tested?

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.