Fix mypy linting issues

[maver1ck]

Description

Fixing mypy linting issues for new mypy version.

Checklist

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!

[sqla-tester]

New Gerrit review created for change a79d47d3acf7ae628ead7ca829bfe1c6f864c3c9: https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/5559

[CaselIT]

thanks!

[sqla-tester]

Gerrit review https://gerrit.sqlalchemy.org/c/sqlalchemy/alembic/+/5559 has been merged. Congratulations! :)