ci: Run sage prover on CI

.cirrus.yml

@@ -322,3 +322,10 @@ task:
   test_script:
     - ./ci/cirrus.sh
   << : *CAT_LOGS
+
+task:
+  name: "sage prover"
+  << : *LINUX_CONTAINER
+  test_script:
+    - cd sage
+    - sage prove_group_implementations.sage

ci/linux-debian.Dockerfile

@@ -19,7 +19,8 @@ RUN apt-get install --no-install-recommends --no-upgrade -y \
         gcc-arm-linux-gnueabihf libc6-dev-armhf-cross libc6-dbg:armhf \
         gcc-aarch64-linux-gnu libc6-dev-arm64-cross libc6-dbg:arm64 \
         gcc-powerpc64le-linux-gnu libc6-dev-ppc64el-cross libc6-dbg:ppc64el \
-        wine gcc-mingw-w64-x86-64
+        wine gcc-mingw-w64-x86-64 \
+        sagemath
 
 # Run a dummy command in wine to make it set up configuration
 RUN wine64-stable xcopy || true