ruby-build 20250529.1

What's Changed

• Mark Ruby 3.1 as EOL by @CamJN in #2536
• Document examples of using custom defs by @jasonkarns in #2537
• Cleanups for truffleruby-dev and truffleruby+graalvm-dev by @eregon in #2538

Full Changelog: v20250516...v20250529.1