CI: Run mypy with --check-untyped-defs

All typing errors found with --check-untyped-defs have been fixed, so let's make mypy stricter now to avoid regressing this.

Depends on and thus includes !2425 (merged). Once it's merged, this can be undrafted and merged.

pmb/helpers/pmaports.py

@@ -13,7 +13,6 @@ from pmb.core.pkgrepo import pkgrepo_iter_package_dirs
 from pmb.helpers import logging
 from pathlib import Path
 from typing import Any
-from collections.abc import Sequence
 
 from pmb.meta import Cache
 import pmb.parse
@@ -46,7 +45,7 @@ def _find_apkbuilds(skip_extra_repos=False) -> dict[str, Path]:
     return apkbuilds
 
 
-def get_list() -> Sequence[str]:
+def get_list() -> list[str]:
     """:returns: list of all pmaport pkgnames (["hello-world", ...])"""
     return list(_find_apkbuilds().keys())