Update sysgen.yml to add risc docker container

Author: mainframed

.github/workflows/sysgen.yml

@@ -89,6 +89,6 @@ jobs:
         with:
           file: Docker/Dockerfile.latest
           context: .
-          platforms: linux/amd64,linux/arm64,linux/s390x
+          platforms: linux/amd64,linux/arm64,linux/s390x,linux/riscv64
           push: true
-          tags: mainframed767/mvsce:latest
+          tags: mainframed767/mvsce:latest