Correct type hint for FunctionElement.table_valued()

Correct type hint for FunctionElement.table_valued()

### Description

The documentation and the type annotations for `TableValueType()` clearly
state that both strings and column expression arguments are accepted
but the annotation omits `str`, which is the most common use case.

### Checklist
This pull request is:

- [x] A documentation / typographical / small typing error fix
	- Good to go, no issue or tests are needed
- [ ] 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.

Closes: #10886
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/10886
Pull-request-sha: 624a97f051b378516518a30d88e7f216456d1c50

Change-Id: I2a1d2eb9b70815c33a27dd238ff2a9f11e5f5a64