Include setup-ocaml version in cache key

Author: cknitt

.github/workflows/ci.yml

@@ -75,6 +75,11 @@ jobs:
 
     runs-on: ${{matrix.os}}
 
+    env:
+      # Also adjust in `uses:` when changed!
+      # This version of setup-ocaml comes with OPAM 2.4.0.
+      SETUP_OCAML_VERSION: 3.4.0
+
     steps:
       - name: "Windows: Set git config"
         if: runner.os == 'Windows'
@@ -141,7 +146,7 @@ jobs:
       # matrix.ocaml_compiler may contain commas
       - name: Get OPAM cache key
         shell: bash
-        run: echo "opam_cache_key=opam-env-v8-${{ matrix.os }}-${{ matrix.ocaml_compiler }}-${{ hashFiles('*.opam') }}" | sed 's/,/-/g' >> $GITHUB_ENV
+        run: echo "opam_cache_key=opam-env-v8-${{ matrix.os }}-${{ env.SETUP_OCAML_VERSION }}-{{ matrix.ocaml_compiler }}-${{ hashFiles('*.opam') }}" | sed 's/,/-/g' >> $GITHUB_ENV
 
       - name: Restore OPAM environment
         id: cache-opam-env
@@ -157,7 +162,7 @@ jobs:
           key: ${{ env.opam_cache_key }}
 
       - name: Use OCaml ${{matrix.ocaml_compiler}}
-        uses: ocaml/setup-ocaml@v3.3.2
+        uses: ocaml/setup-ocaml@v3.4.0
         if: steps.cache-opam-env.outputs.cache-hit != 'true'
         with:
           ocaml-compiler: ${{matrix.ocaml_compiler}}