License GitHub community-health workflows as MPL-2.0 (fix reuse lint)

The reuse-lint check failed because the three standards-adopted
community-health workflow stubs (hypatia-scan.yml, governance.yml,
scorecard.yml) declared a bare `SPDX-License-Identifier: PMPL-1.0-or-later`.
PMPL is a custom license, so REUSE rejects the bare identifier (custom
licenses must use a `LicenseRef-` prefix); and REUSE.toml already aggregates
`.github/**` + `**/*.yml` as MPL-2.0 on top, leaving PMPL "used" but invalid.

Per maintainer direction, license the GitHub community-health files as
MPL-2.0 (the estate's code/config license) with the standard two-line SPDX
header, keeping MPL-2.0 + CC-BY-SA-4.0 as the repo's two licenses. PMPL is no
longer used, so no PMPL license text file is required.

Verified locally with `reuse lint`: compliant with REUSE 3.3
(Used licenses: CC-BY-SA-4.0, MPL-2.0; 0 bad / 0 missing / 0 unused;
775/775 files covered).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017nyxs8RgqZa72PzrTu3L75

Author: claude

.github/workflows/governance.yml

@@ -1,4 +1,5 @@
-# SPDX-License-Identifier: PMPL-1.0-or-later
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+# SPDX-License-Identifier: MPL-2.0
 name: Governance
 
 on:

.github/workflows/hypatia-scan.yml

@@ -1,4 +1,5 @@
-# SPDX-License-Identifier: PMPL-1.0-or-later
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+# SPDX-License-Identifier: MPL-2.0
 name: Hypatia Security Scan
 
 on:

.github/workflows/scorecard.yml

@@ -1,4 +1,5 @@
-# SPDX-License-Identifier: PMPL-1.0-or-later
+# SPDX-FileCopyrightText: 2026 Jonathan D.A. Jewell <j.d.a.jewell@open.ac.uk>
+# SPDX-License-Identifier: MPL-2.0
 name: OSSF Scorecard
 
 on: