Fixed an invalid syntax in an except statement

Fixed an invalid syntax in an except statement

### Description

As the title suggests, I have fixed an invalid syntax in the docs for an `except` statement while reading the unusual.

### Checklist
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This pull request is:

- [x] A documentation / typographical 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: #8715
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/8715
Pull-request-sha: e8be2bc4a5401ab2a5a0fc1d2e50d41fa437ae80

Change-Id: If8512bf1853f7cdb1ae655f0945cd922fff6fbce