Fix CI: silence false-positive ShellCheck/EditorConfig findings

- podman-common.sh: file-wide shellcheck disable=SC2034 for its
  constants, which are intentionally defined for other scripts to
  source, not used within the file itself (ShellCheck can't see
  cross-file usage in that direction). Confirmed as the actual cause
  of the failing ShellCheck job via the real Gitea Actions log.
- podman-storage.sh: use the retry counter in cmd_unmount's log
  message instead of leaving it genuinely unused (real SC2034 hit,
  not a false positive).
- lint.yml: replace the editorconfig-checker/action-* marketplace
  action with a pinned, checksum-verified direct binary download —
  more robust than relying on third-party action resolution on
  self-hosted Gitea Actions runners — and disable its IndentSize
  check, which false-positives on Markdown's nested-list indentation
  and shell heredoc bodies. scripts/dev/lint.sh mirrors the same check
  for local use. All three lint.yml jobs verified passing locally.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

plugin/sbin/podman-storage.sh

@@ -144,6 +144,7 @@ cmd_unmount() {
       podman_log "storage: unmounted"
       return 0
     fi
+    podman_log "storage: unmount busy, retrying (attempt $attempt/5)"
     sleep 1
   done