ci, gha: Run "SageMath prover" job on GitHub Actions

.cirrus.yml

@@ -371,10 +371,3 @@ task:
     - g++ -Werror include/*.h
     - clang -Werror -x c++-header include/*.h
     - /opt/msvc/bin/x64/cl.exe -c -WX -TP include/*.h
-
-task:
-  name: "sage prover"
-  << : *LINUX_CONTAINER
-  test_script:
-    - cd sage
-    - sage prove_group_implementations.sage

.github/workflows/ci.yml

@@ -37,3 +37,19 @@ jobs:
           build\src\RelWithDebInfo\bench_ecmult.exe
           build\src\RelWithDebInfo\bench_internal.exe
           build\src\RelWithDebInfo\bench.exe
+
+  sage:
+    name: "SageMath prover"
+    runs-on: ubuntu-latest
+    container:
+      image: sagemath/sagemath:latest
+      options: --user root
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: CI script
+        run: |
+          cd sage
+          sage prove_group_implementations.sage

ci/linux-debian.Dockerfile

@@ -21,8 +21,7 @@ RUN apt-get update && apt-get install --no-install-recommends -y \
         gcc-aarch64-linux-gnu libc6-dev-arm64-cross libc6-dbg:arm64 \
         gcc-powerpc64le-linux-gnu libc6-dev-ppc64el-cross libc6-dbg:ppc64el \
         gcc-mingw-w64-x86-64-win32 wine64 wine \
-        gcc-mingw-w64-i686-win32 wine32 \
-        sagemath
+        gcc-mingw-w64-i686-win32 wine32
 
 WORKDIR /root