ci: pin GitHub Actions to SHA digests (fix zizmor unpinned-uses) (#33)

Author: lhoupert

.github/workflows/deploy_mkdocs.yaml

@@ -11,10 +11,10 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout main
-        uses: actions/checkout@v6
+        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6
 
       - name: Install uv
-        uses: astral-sh/setup-uv@v7
+        uses: astral-sh/setup-uv@37802adc94f370d6bfd71619e3f0bf239e1f3b78 # v7
         with:
           version: "0.9.*"
           enable-cache: true