fix: add permissions and SHA-pin actions in mirror.yml

- Add permissions: read-all for Token-Permissions check
- Pin actions/checkout to SHA for Pinned-Dependencies check

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: Jonathan D.A. Jewell

.github/workflows/mirror.yml

@@ -7,14 +7,16 @@ on:
       - 'v*'
   workflow_dispatch:
 
+permissions: read-all
+
 jobs:
   mirror-gitlab:
     runs-on: ubuntu-latest
     if: ${{ vars.GITLAB_MIRROR_ENABLED == 'true' }}
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           fetch-depth: 0
 
@@ -33,7 +35,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
         with:
           fetch-depth: 0