ci: bump rb_sys floor to 0.9.124 for Ruby 4 platform gems

Author: kateinoigakukun

.github/workflows/build-gems.yml

@@ -56,7 +56,8 @@ jobs:
           fi
 
           # Ruby 4.0 cross-compilation support requires newer rb-sys/rake-compiler-dock.
-          min_version="0.9.126"
+          # 0.9.124 has published docker images across all target platforms.
+          min_version="0.9.124"
           if [ "$(printf '%s\n' "$version" "$min_version" | sort -V | tail -n1)" != "$version" ]; then
             version="$min_version"
           fi

Gemfile

@@ -7,7 +7,7 @@ gemspec
 group :development do
   gem "rake"
   gem "rake-compiler"
-  gem "rb_sys", "0.9.108"
+  gem "rb_sys", "0.9.124"
   gem "rdoc", "~> 7.0"
 end