Use digest for actions/checkout in all workflows

Signed-off-by: Erik Godding Boye <[email protected]>

Author: erikgb

.github/workflows/check.yaml

@@ -8,7 +8,7 @@ jobs:
   pull-cert-manager-website-verify:
     runs-on: ubuntu-22.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
       - uses: actions/setup-node@v4
         with:
           node-version: 20