fix(ci): pin the long-tail actions and retire scorecard-enforcer.yml

Closes the two residual `governance` failures left by the first sweep:

* `Workflow security linter` reported "Found unpinned actions" for actions
  outside the first pass's pin map (docker/*, slsa, julia-actions, softprops,
  ipdxco, codeql upload-sarif). Floating branch refs (@main / @master) are
  left alone on purpose — pinning those is a version decision.
* `Check Workflow Staleness` errors on `scorecard-enforcer.yml` by name (it
  is retired in favour of scorecard.yml -> standards scorecard-reusable.yml)
  and separately on Scorecard uploading SARIF to Code Scanning. Removing the
  retired file resolves both. It is removed only where scorecard.yml already
  exists, so Scorecard coverage is retained.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: hyperpolymath