Fix release pin sed delimiter

[dceoy]

Summary

• use a non-conflicting sed delimiter when updating reusable workflow pins
• avoid treating the version comment # or the (bot|review) alternation as the substitution delimiter

Root cause

The post-release workflow used # as the sed delimiter while also emitting # ${RELEASE_TAG} in the replacement text, causing sed: unknown option to 's'.

Validation

• reproduced the failing expression locally
• verified the replacement with , as the delimiter updates the pinned SHA and version comment correctly
• branch diff is limited to one line in .github/workflows/post-release.yml

[dceoy]

Reviewed the one-line workflow fix. No actionable issues found. The delimiter change avoids conflicts with both the literal version-comment # and the (bot|review) alternation, while preserving the existing match-count guards and replacement behavior. CI/CD passes on the reviewed head commit.