Adjust TypeError message to Python 3.15

Adjust TypeError message to Python 3.15

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

### Description
The `.fromisoformat()` error message tested in `test_no_string()` changed in Python 3.15, this fixes the test.

See #13308 for the `rel_2_0` branch.

### 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 / small typing error fix
	- Good to go, no issue or tests are needed
- [x] A short code fix (in a test, therefore I didn’t create an issue)
	- 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: #13307
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/13307
Pull-request-sha: 90bc13fc416ea45ba5429d5f8ecffc24b108c1b1

Change-Id: I461d71b0fad18fa4f108102bb1c22c0e980fc70e