fix error in test_round_trip for TimeTest with mysql+pyodbc

fix error in test_round_trip for TimeTest with mysql+pyodbc

Fixes: #4879
### Description
create mysql+pyodbc-specific `_pyodbcTIME` class to avoid error thrown by `result_processor` in the (more) generic mysql/types.py.

### Checklist
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This pull request is:

- [ ] A documentation / typographical error fix
	- Good to go, no issue or tests are needed
- [x] 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: #4880
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/4880
Pull-request-sha: 2e4c468c3ad685d6573e0d9755ba97a28df50b6c

Change-Id: Ib5c5b0971969c2a9870b7f43d06703618cfc56f7
(cherry picked from commit f94940e4d88b4011fd089bed37cebb76acb1a385)