Fix docs typo: subuqery -> subquery

Fix docs typo: subuqery -> subquery

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### Description
Fixes #5839
(sorry, realized just now that an issue wasn't required)

### 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: #5840
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/5840
Pull-request-sha: b6f6af929fab4dab771565f6373b0275acbca793

Change-Id: I0b4c9b2d893e8141ee1cd21742a9b111fe371bac