connection.close() returns None when called from async function - await fails

### Describe the bug

see code to reproduce -

1) define async function
2) call connection = await aiomysql.connect(...)
3) execute some operation (SELECT 1)
4) call await connection.close()
5) app crashed

### To Reproduce

Execute attached python script

### Expected behavior

connection.close() should be returning a waitable object for await and not None

### Logs/tracebacks

```python-traceback
python test-aiomysql-close
2025-07-31 10:53:50,009 INFO : Attempting to connect to maria:3306...
2025-07-31 10:53:50,017 INFO : Successfully connected.
2025-07-31 10:53:50,018 INFO : Dummy query executed successfully.
2025-07-31 10:53:50,018 INFO : Type of conn.close() result (before await):
2025-07-31 10:53:50,018 INFO : Value of conn.close() result (before await): None
2025-07-31 10:53:50,018 INFO : Attempting to await conn.close()...
2025-07-31 10:53:50,018 ERROR : An error occurred: object NoneType can't be used in 'await' expression
Traceback (most recent call last):
File "/home/phil/temp/test-aiomysql-close", line 42, in test_close_behavior
await close_awaitable
TypeError: object NoneType can't be used in 'await' expression
```

### Python Version

```console
$ python --version
Python 3.12.3
```

### aiomysql Version

```console
$ python -m pip show aiomysql
Name: aiomysql
Version: 0.2.0
Summary: MySQL driver for asyncio.
Home-page: https://github.com/aio-libs/aiomysql
Author: Nikolay Novik
Author-email: nickolainovik@gmail.com
License: MIT
Location: /home/phil/dev/archiver/venv/lib/python3.12/site-packages
Requires: PyMySQL
Required-by: async-sqlalchemy
```

### PyMySQL Version

```console
$ python -m pip show PyMySQL
Name: PyMySQL
Version: 1.1.1
Summary: Pure Python MySQL Driver
Home-page:
Author:
Author-email: Inada Naoki , Yutaka Matsubara
License: MIT License
Location: /home/phil/dev/archiver/venv/lib/python3.12/site-packages
Requires:
Required-by: aiomysql
```

### SQLAlchemy Version

```console
$ python -m pip show sqlalchemy
Name: SQLAlchemy
Version: 2.0.40
Summary: Database Abstraction Library
Home-page: https://www.sqlalchemy.org
Author: Mike Bayer
Author-email: mike_mp@zzzcomputing.com
License: MIT
Location: /home/phil/dev/archiver/venv/lib/python3.12/site-packages
Requires: greenlet, typing-extensions
Required-by: async-sqlalchemy
```

### OS

cat /etc/os-release
PRETTY_NAME="Ubuntu 24.04.2 LTS"
NAME="Ubuntu"
VERSION_ID="24.04"
VERSION="24.04.2 LTS (Noble Numbat)"
VERSION_CODENAME=noble
ID=ubuntu
ID_LIKE=debian
HOME_URL="https://www.ubuntu.com/"
SUPPORT_URL="https://help.ubuntu.com/"
BUG_REPORT_URL="https://bugs.launchpad.net/ubuntu/"
PRIVACY_POLICY_URL="https://www.ubuntu.com/legal/terms-and-policies/privacy-policy"
UBUNTU_CODENAME=noble
LOGO=ubuntu-logo

### Database type and version

```console
SELECT VERSION();
'10.11.11-MariaDB-0ubuntu0.24.04.2'
```

### Additional context

Add code to application to ensure the db is created before sqlalchemy creates tables

### Code of Conduct

- [x] I agree to follow the aio-libs Code of Conduct