Improved PEP-484 for AsyncSession.run_sync

Improved PEP-484 for AsyncSession.run_sync

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### Description
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I don't think this needs any test added.

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix
	- please include the issue number, and create an issue if none exists, which
	  must include a complete example of the issue.  one line code fixes without an
	  issue and demonstration will not be accepted.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.   one line code fixes without tests will not be accepted.
- [ ] A new feature implementation
	- please include the issue number, and create an issue if none exists, which must
	  include a complete example of how the feature would look.
	- Please include: `Fixes: #<issue number>` in the commit message
	- please include tests.

Fixes: #5777
**Have a nice day!**

Closes: #5778
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5778
Pull-request-sha: 618ddc84d27b9b67f9ae78fd457f94feff1ce160

Change-Id: Id46f70ddc14e8f8d7e402a4b3ce7e934509bef24