[CI] [Alpine] Use dev version of Coq

From https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/57766#note_365103

.github/workflows/coq-alpine.yml

@@ -39,6 +39,22 @@ jobs:
         branch: ${{ matrix.alpine }}
         extra-repositories: https://dl-cdn.alpinelinux.org/alpine/edge/testing
         packages: git make jq gcc musl-dev python3 ocaml ocaml-findlib ghc cabal coq ocaml-zarith bash
+    # next two steps as per https://gitlab.alpinelinux.org/alpine/aports/-/merge_requests/57766#note_365103
+    - name: Download development Coq
+      shell: alpine.sh {0}
+      run: |
+        mkdir -p MR
+        wget 'https://gitlab.alpinelinux.org/JasonGross/aports/-/jobs/1222367/artifacts/download?file_type=archive' -O MR.zip
+        unzip MR.zip -d MR
+        ls -la MR
+        find MR
+    - name: Set up development Coq
+      shell: alpine.sh --root {0}
+      run: |
+        mv MR/keys/*.pub /etc/apk/keys/
+        printf "\n%s\n" "$(cd MR/packages && pwd)" >> /etc/apk/repositories
+        apk update
+        apk add coq --no-confirm --reinstall
     - name: chroot build params
       shell: alpine.sh {0}
       run: etc/ci/describe-system-config.sh