ci: pin rb-sys-dock image tag to published 0.9.124

Author: kateinoigakukun

.github/workflows/build-gems.yml

@@ -71,7 +71,10 @@ jobs:
           RB_SYS_VERSION: ${{ steps.rb-sys.outputs.version }}
         run: |
           gem install rb_sys -v "$RB_SYS_VERSION"
-          rb-sys-dock --platform "$PLATFORM" --directory . --ruby-versions "$RUBY_VERSIONS" --build
+          # rb-sys gem and docker image tags are released independently.
+          # Use the latest image tag currently published for all platforms.
+          RCD_IMAGE_VERSION="0.9.124" \
+            rb-sys-dock --platform "$PLATFORM" --directory . --ruby-versions "$RUBY_VERSIONS" --build
 
           gem_path="$(find ./pkg -name "*-${PLATFORM}.gem" | head -n1)"
           if [ -z "$gem_path" ]; then