add CPU image matrix entries to CI

Author: HarshaSatyavardhan

.github/workflows/docker.yml

@@ -29,6 +29,14 @@ jobs:
             path: docker/Dockerfile
             tag_base: arm64
             name: mirage-git
+          - platform: ubuntu-latest
+            path: docker/Dockerfile.cpu
+            tag_base: amd64
+            name: mirage-git-cpu
+          - platform: ubuntu-24.04-arm
+            path: docker/Dockerfile.cpu
+            tag_base: arm64
+            name: mirage-git-cpu
 
     runs-on: ${{ matrix.platform }}
     environment: docker