Pin GitHub Actions to commit hashes for improved security

Replace version tags with full commit hashes in spam detection workflow:
- actions/checkout@v4 → @08eba0b27e820071cde6df949e0beb9ba4906955 (v4.3.0)
- github/ai-moderator@v1 → @6bcdb2a79c2e564db8d76d7d4439d91a044c4eb6 (v1)

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: mcollina

.github/workflows/spam-detect.yml

@@ -16,8 +16,8 @@ jobs:
       models: read
       contents: read
     steps:
-      - uses: actions/checkout@v4
-      - uses: github/ai-moderator@v1
+      - uses: actions/checkout@08eba0b27e820071cde6df949e0beb9ba4906955 # v4.3.0
+      - uses: github/ai-moderator@6bcdb2a79c2e564db8d76d7d4439d91a044c4eb6 # v1
         with:
           token: ${{ secrets.GITHUB_TOKEN }}
           spam-label: 'spam'