fix(license): restore MPL-2.0 on secret-scanner.yml + scorecard.yml

Both workflow files carried SPDX PMPL-1.0, applied by a prior bulk license
sweep (see CHANGELOG: "global AGPL-3.0-or-later -> PMPL-1.0-or-later
replacement"). Per estate policy PMPL is reserved for palimpsest-license,
palimpsest-plasma, and consent-aware-http only; empty-linter is a sole-owner
repo and defaults to MPL-2.0 (matching every other workflow here). The
identifier was also malformed (PMPL-1.0 vs the repo's PMPL-1.0-or-later).

Owner-approved, per-file correction; no other files touched.

https://claude.ai/code/session_01EqEysvTPzPwhS9ZGY7EYdr

Author: claude

.github/workflows/scorecard.yml

@@ -1,5 +1,5 @@
 # // Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
-# SPDX-License-Identifier: PMPL-1.0
+# SPDX-License-Identifier: MPL-2.0
 name: Scorecards supply-chain security
 
 on:

.github/workflows/secret-scanner.yml

@@ -1,5 +1,5 @@
 # // Copyright (c) Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
-# SPDX-License-Identifier: PMPL-1.0
+# SPDX-License-Identifier: MPL-2.0
 name: Secret Scanner
 on:
   pull_request: