disable opam cache in CI

.github/workflows/build.yml

@@ -31,20 +31,11 @@ jobs:
           git submodule update --init test/script/reference
           git submodule update --init test/c/collections-c/files
           mv .git .git.tmp # prevents opam from checking-out submodules
-      - name: cache
-        id: cache-opam
-        uses: actions/cache@v4
-        env:
-          cache-name: cache-opam-build
-        with:
-          path: |
-            ~/work/owi/owi/_opam/
-          key: ${{ runner.os }}-build-${{ matrix.ocaml-compiler }}-${{ env.cache-name }}-${{ hashFiles('**/*.opam') }}
       - name: setup-ocaml
         uses: ocaml/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
-          dune-cache: true
+          dune-cache: false
           opam-pin: true
           allow-prerelease-opam: false
       - name: depext
@@ -62,12 +53,10 @@ jobs:
           fi
           opam install . --depext-only --with-test --with-doc
       - name: setup
-        if: steps.cache-opam.outputs.cache-hit != 'true'
         run: |
           opam install . --deps-only --with-test --with-doc
           opam install smtml z3
           opam install ocamlformat
-          opam clean --switch-cleanup
       - name: build
         run: |
           if [ "$RUNNER_OS" == "macOS" ]; then