🔒️(ci) pin every action to a full commit hash

A tag and a branch both move, so actions/checkout@v6 and
numerique-gouv/action-trivy-cache@main ran whatever the owner had last
pushed. Each of the 65 uses now names a 40-character commit, with the
version it resolved to in a trailing comment.

dependabot.yml keeps the hash and that comment moving together.

.github/workflows/release-helm-chart.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v6
+        uses: actions/checkout@d23441a48e516b6c34aea4fa41551a30e30af803 # v6.1.0
         with:
           fetch-depth: 0
 
@@ -21,12 +21,12 @@ jobs:
         run: rm -rf ./src/helm/extra
 
       - name: Install Helm
-        uses: azure/setup-helm@v4
+        uses: azure/setup-helm@1a275c3b69536ee54be43f2070a358922e12c8d4 # v4.3.1
         env:
           GITHUB_TOKEN: "${{ secrets.GITHUB_TOKEN }}"
 
       - name: Publish Helm charts
-        uses: numerique-gouv/helm-gh-pages@add-overwrite-option
+        uses: numerique-gouv/helm-gh-pages@2cf477ae49d7c70037ceb1685803f4f7bad9b981 # add-overwrite-option
         with:
           charts_dir: ./src/helm
           linting: on