Add missing type hints in core/dbt/task/clean.py

[QMalcolm]

Housekeeping

• I am a maintainer of dbt-core

Short description

We're putting some effort into improving our typing. There are two type errors in core/dbt/task/clean.py, we should fix them.

core/dbt/task/clean.py:19: error: Function is missing a return type annotation  [no-untyped-def]
core/dbt/task/clean.py:19: note: Use "-> None" if function does not return a value
core/dbt/task/clean.py:49: error: Call to untyped function "warn" in typed context  [no-untyped-call]

Acceptance criteria

Fix the typing issues

Suggested Tests

N/A

Impact to Other Teams

None

Will backports be required?

No

Context

No response