CI: Fix pushing Docker images automatically (#353)

Author: henrybear327

.github/workflows/main.yml

@@ -155,6 +155,7 @@ jobs:
         if: ${{ github.event_name == 'push'}}
         uses: docker/build-push-action@v5
         with:
+          push: true
           context: .
           platforms: linux/amd64,linux/arm64/v8
           tags: sysprog21/rv32emu:latest, sysprog21/rv32emu:${{ env.short_hash }}