Fix Windows CI

Error was:

    line 1: $'\r': command not found

See: ocaml/setup-ocaml#815 (comment)

.github/workflows/main.yml

@@ -25,16 +25,6 @@ jobs:
         uses: actions/checkout@v3
 
       - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        if: runner.os == 'Windows'
-        uses: ocaml/setup-ocaml@v3
-        with:
-          ocaml-compiler: ${{ matrix.ocaml-compiler }}
-          opam-repositories: |
-            opam-repository-mingw: https://github.com/ocaml-opam/opam-repository-mingw.git#sunset
-            default: https://github.com/ocaml/opam-repository.git
-
-      - name: Use OCaml ${{ matrix.ocaml-compiler }}
-        if: runner.os != 'Windows'
         uses: ocaml/setup-ocaml@v3
         with:
           ocaml-compiler: ${{ matrix.ocaml-compiler }}
@@ -44,6 +34,7 @@ jobs:
         shell: bash
         env:
           CAPNP_VERSION: 1.0.1
+          SHELLOPTS: igncr
         run: |
           curl -LO https://capnproto.org/capnproto-c++-win32-$CAPNP_VERSION.zip && \
           unzip -j capnproto-c++-win32-$CAPNP_VERSION.zip capnproto-tools-win32-$CAPNP_VERSION/capnp.exe -d /usr/bin