Update workflow

Author: andersfugmann

.github/workflows/workflow.yml

@@ -6,31 +6,36 @@ on:
   pull_request:
   workflow_dispatch:
 
+permissions:
+  contents: read
+
 concurrency:
   group: ${{ github.workflow }}-${{ github.ref }}
   cancel-in-progress: true
 
 jobs:
   build:
+    timeout-minutes: 30
     strategy:
       matrix:
         os:
           - ubuntu-latest
         ocaml-compiler:
           - 5
-          - 4
+          - 4 # latest OCaml 4 release
           - 4.11.0
 
     runs-on: ${{ matrix.os }}
 
     steps:
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@34e114876b0b11c390a56381ad16ebd13914f8d5 # v4
 
       - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        uses: ocaml/setup-ocaml@v3
+        uses: ocaml/setup-ocaml@e32b06a3e831ff2fbc6f08cf35be2085e3918014 # v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
+          dune-cache: true
 
       - name: Install system dependencies
         run: opam install conf-protoc --yes