[CT-2986] Fix untyped functions in task/runnable.py (mypy warning)

[emmyoop]

Problem

When we hit a mypy error the console is flooded with mypy warnings as well. Clean up the warning to improve developer experience.

Reproduction

Simply force a mypy error (change types) and the warnings will be generated.

Relevant Output

core/dbt/task/runnable.py:71: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:74: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:76: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:77: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:78: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:79: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:80: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:173: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:174: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/task/runnable.py:203: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]