fix: resolve ruff lint errors (E402, F401, F821)

- check_versions.py: restore correct file (import re was placed before
  shebang causing E402 for all following imports; missing 'client' in
  kubernetes import causing F821 at line 236)
- request_upgrades.py: remove unused 're' import and unused 'client'
  from kubernetes import (only 'config' is needed here)
- web.py: remove unused 'os' import

request_upgrades.py

@@ -8,7 +8,7 @@ the tag updates. ArgoCD auto-syncs from there — no direct kubectl patching.
 """
 
 import os
-import re
+
 import shutil
 import subprocess
 import tempfile
@@ -18,7 +18,7 @@ from datetime import datetime, timezone
 from pathlib import Path
 
 import requests
-from kubernetes import client, config
+from kubernetes import config
 from packaging.version import Version, InvalidVersion
 
 from check_versions import (