[ruby/rack] Set timeslice to 10ms (#10074)

By default this is set to 100ms.
https://github.com/ruby/ruby/pull/11981

frameworks/Ruby/rack/rack.dockerfile

@@ -2,6 +2,7 @@ FROM ruby:3.5-rc
 
 ENV RUBY_YJIT_ENABLE=1
 ENV RUBY_MN_THREADS=1
+ENV RUBY_THREAD_TIMESLICE=10
 
 # Use Jemalloc
 RUN apt-get update && \