Fix typing issues

[CaselIT]

Some issues when using types in code have come up:

• [ ] https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/3447/comment/83a4e453_d20a3bbd/
• [x] https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/3447/comment/569393c5_a3de5fd8/

[zzzeek]

and also (will open a separate issue, this is easier to fix hopefully): https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/3525/2/lib/sqlalchemy/util/_concurrency_py3k.py#19

[zzzeek]

for https://gerrit.sqlalchemy.org/c/sqlalchemy/sqlalchemy/+/3447/comment/569393c5_a3de5fd8/ this is #33

[zzzeek]

the other issue is #12