Improved PEP-484 for AsyncSession.run_sync

<!-- Provide a general summary of your proposed changes in the Title field above -->

### Description
<!-- Describe your changes in detail -->
I don't think this needs any test added.

### Checklist
<!-- go over following points. check them with an `x` if they do apply, (they turn into clickable checkboxes once the PR is submitted, so no need to do everything at once)

-->

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

1 files changed, 5 insertions, 2 deletions

diff --git a/lib/sqlalchemy/ext/asyncio/session.py b/lib/sqlalchemy/ext/asyncio/session.py
index 4ae1fb385..c21b67954 100644
--- a/lib/sqlalchemy/ext/asyncio/session.py
+++ b/lib/sqlalchemy/ext/asyncio/session.py
@@ -1,7 +1,7 @@
-from typing import Any
 from typing import Callable
 from typing import Mapping
 from typing import Optional
+from typing import TypeVar
 
 from . import engine
 from . import result as _result
@@ -14,6 +14,9 @@ from ...sql import Executable
 from ...util.concurrency import greenlet_spawn
 
 
+T = TypeVar("T")
+
+
 @util.create_proxy_methods(
     Session,
     ":class:`_orm.Session`",
@@ -102,7 +105,7 @@ class AsyncSession:
             with_for_update=with_for_update,
         )
 
-    async def run_sync(self, fn: Callable, *arg, **kw) -> Any:
+    async def run_sync(self, fn: Callable[..., T], *arg, **kw) -> T:
         """Invoke the given sync callable passing sync self as the first
         argument.