add ci image build step

Author: TheDeepestSpace

.github/workflows/ci.yaml

@@ -4,10 +4,58 @@ on:
   pull_request:
 
 jobs:
+  build_ci_image:
+    runs-on: ubuntu-latest
+    outputs:
+      image-tag: ${{ steps.meta.outputs.tags }}
+      image-digest: ${{ steps.build.outputs.digest }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+
+      - name: Login to GitHub Container Registry
+        uses: docker/login-action@v3
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Extract metadata
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: ghcr.io/utoss/risc-v
+          tags: |
+            type=ref,event=branch,prefix=ci-
+            type=ref,event=pr,prefix=ci-
+            type=raw,value=latest,prefix=ci,enable={{is_default_branch}}
+
+      - name: Build and push Docker image
+        id: build
+        uses: docker/build-push-action@v5
+        with:
+          context: .
+          file: ./Dockerfile.ci
+          push: true
+          tags: ${{ steps.meta.outputs.tags }}
+          labels: ${{ steps.meta.outputs.labels }}
+          platforms: linux/amd64
+          cache-from: |
+            type=gha
+            type=registry,ref=ghcr.io/utoss/risc-v:buildcache
+          cache-to: |
+            type=gha,mode=max
+            type=registry,ref=ghcr.io/utoss/risc-v:buildcache,mode=max
+
   build_and_test:
+    needs: build_ci_image
     runs-on: ubuntu-latest
     container:
-      image: ghcr.io/utoss/risc-v:ci
+      image: ${{ needs.build_ci_image.outputs.image-tag }}
 
     steps:
       - name: Checkout code