Don't enable io_write hook on Ruby < 3.3.1 as it's buggy. (#303)

.github/workflows/coverage.yaml

@@ -29,6 +29,9 @@ jobs:
           - os: ubuntu
             ruby: "3.3"
             selector: URing
+          - os: ubuntu
+            ruby: "head"
+            selector: URing
 
     steps:
     - uses: actions/checkout@v4

lib/async/scheduler.rb

@@ -212,7 +212,7 @@ def io_read(io, buffer, length, offset = 0)
 				timer&.cancel
 			end
 
-			if RUBY_ENGINE != "ruby" || RUBY_VERSION >= "3.3.0"
+			if RUBY_ENGINE != "ruby" || RUBY_VERSION >= "3.3.1"
 				def io_write(io, buffer, length, offset = 0)
 					fiber = Fiber.current
 

test/io.rb

@@ -74,4 +74,18 @@
 			expect(input.wait_readable(0)).to be_nil
 		end
 	end
+
+	describe '/dev/null' do
+		# Ruby < 3.3.1 will fail this test with the `io_write` scheduler hook enabled, as it will try to io_wait on /dev/null which will fail on some platforms (kqueue).
+		it "can write to /dev/null" do
+			out = File.open("/dev/null", "w")
+
+			# Needs to write about 8,192 bytes to trigger the internal flush:
+			1000.times do
+				out.puts "Hello World!"
+			end
+		ensure
+			out.close
+		end
+	end
 end