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-common.sh

@@ -22,6 +22,16 @@
 # that set their own error-handling mode, and a library changing its
 # caller's shell options would be a surprising action at a distance.
 
+# shellcheck disable=SC2034
+# This whole file is a "library" of constants and functions for OTHER
+# scripts to `source` — see the header above. ShellCheck analyzes each file
+# in isolation and has no way to see that e.g. $PODMAN_AUTOSTART_FILE is
+# used in podman-autostart.sh, not here, so it flags every constant below
+# as "appears unused". That is a false positive for this file's actual
+# role; disabling SC2034 file-wide (this directive, placed before any code,
+# applies to the whole file per ShellCheck's own rules) is more honest than
+# scattering 15+ identical per-line suppressions.
+
 # -----------------------------------------------------------------------------
 # Path constants.
 #