Update Ruby Docker image for aarch64 tests.

PiperOrigin-RevId: 949709833

Author: Rachel Goldfinger

.github/workflows/test_ruby.yml

@@ -122,7 +122,7 @@ jobs:
         if: ${{ inputs.continuous-run }}
         uses: protocolbuffers/protobuf-ci/docker@v5
         with:
-          image: arm64v8/ruby:3.2.11-bookworm
+          image: ruby:3.2.11-bookworm
           credentials: ${{ secrets.GAR_SERVICE_ACCOUNT }}
           platform: linux/arm64
           command: >-