Upgrade to Oracle Database 23c Free

Upgrade to Oracle Database 23c Free

### Description
This PR updates the unittest ReadMe and `setup.cfg` to use Oracle Database Free, the successor to Oracle Database XE.

### Checklist

This pull request is:

- [ ] 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.

**Have a nice day!**

Closes: #10658
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/10658
Pull-request-sha: 1cfb2d3a7f688a4b887182d2485b7d60f12eb013

Change-Id: Id37f6607572c1fdb12d507cd9336800d4d8b0cf3