Retry IO.select with a longer timeout on flaky platforms (#16542)

On MinGW (Windows), pipe readiness after syswrite may not be
immediately visible to IO.select with timeout 0, causing a
spurious nil return. Retry with a longer timeout to handle this.

https://github.com/ruby/ruby/actions/runs/23519269557/job/68458831324?pr=16262

Author: k0kubun

core/io/select_spec.rb

@@ -18,6 +18,10 @@
     @wr.syswrite("be ready")
     IO.pipe do |_, wr|
       result = IO.select [@rd], [wr], nil, 0
+      unless result
+        # On some platforms (e.g., Windows), pipe readiness may not be immediate
+        result = IO.select [@rd], [wr], nil, 2
+      end
       result.should == [[@rd], [wr], []]
     end
   end