[CT-2973] Fix untyped functions in semver.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/semver.py:111: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]
core/dbt/semver.py:112: note: By default the bodies of untyped functions are not checked, consider using --check-untyped-defs  [annotation-unchecked]