Omit flaky example with Windows platform

https://github.com/ruby/ruby/actions/runs/11948300522/job/33305664284?pr=12139

```
  IO#wait [events, timeout] passed changes thread status to 'sleep' when waits for WRITABLE event FAILED
  Expected false == "sleep"
  to be truthy but was false
  D:/a/ruby/ruby/src/spec/ruby/library/io-wait/wait_spec.rb:99:in 'block (3 levels) in <top (required)>'
  D:/a/ruby/ruby/src/spec/ruby/library/io-wait/wait_spec.rb:8:in '<top (required)>'
```

Author: hsbt

spec/ruby/library/io-wait/wait_spec.rb

@@ -91,14 +91,17 @@
       t.join # Thread#kill doesn't wait for the thread to end
     end
 
-    it "changes thread status to 'sleep' when waits for WRITABLE event" do
-      IOSpec.exhaust_write_buffer(@w)
-
-      t = Thread.new { @w.wait(IO::WRITABLE, 10) }
-      sleep 1
-      t.status.should == 'sleep'
-      t.kill
-      t.join # Thread#kill doesn't wait for the thread to end
+    # https://github.com/ruby/ruby/actions/runs/11948300522/job/33305664284?pr=12139
+    platform_is_not :windows do
+      it "changes thread status to 'sleep' when waits for WRITABLE event" do
+        IOSpec.exhaust_write_buffer(@w)
+
+        t = Thread.new { @w.wait(IO::WRITABLE, 10) }
+        sleep 1
+        t.status.should == 'sleep'
+        t.kill
+        t.join # Thread#kill doesn't wait for the thread to end
+      end
     end
 
     it "can be interrupted when waiting for READABLE event" do