fix: resolve ruff lint errors (unused imports and variable)

check_versions.py

@@ -1,3 +1,4 @@
+import re
 #!/usr/bin/env python3
 """
 k8s-version-tracker: Weekly Kubernetes image version checker and Mattermost notifier.
@@ -8,8 +9,6 @@ notification with the weekly report.
 """
 
 import os
-import re
-import json
 import logging
 import subprocess
 from dataclasses import dataclass, field
@@ -17,7 +16,7 @@ from typing import Optional
 from datetime import datetime, timezone
 
 import requests
-from kubernetes import client, config
+from kubernetes import config
 from packaging.version import Version, InvalidVersion
 
 logging.basicConfig(level=logging.INFO, format="%(asctime)s %(levelname)s %(message)s")
@@ -121,7 +120,6 @@ def parse_image_ref(image: str) -> ImageInfo:
 def _semver_tags(tags: list[str], current_tag: str) -> Optional[str]:
     """From a list of tags, return the latest stable semver tag comparable to current."""
     norm = current_tag.lstrip("v")
-    has_v_prefix = current_tag.startswith("v")
 
     # Detect suffix pattern (e.g. '-alpine', '-amd64')
     suffix_match = re.search(r"(-[a-zA-Z][a-zA-Z0-9._-]*)$", norm)