Restrict async to MRI Ruby only

Author: seuros

.github/workflows/test.yaml

@@ -28,12 +28,6 @@ jobs:
         experimental: [false]
 
         include:
-          - os: ubuntu
-            ruby: truffleruby
-            experimental: true
-          - os: ubuntu
-            ruby: jruby
-            experimental: true
           - os: ubuntu
             ruby: head
             experimental: true

async.gemspec

@@ -24,6 +24,7 @@ Gem::Specification.new do |spec|
 	spec.files = Dir.glob(["{lib}/**/*", "*.md"], File::FNM_DOTMATCH, base: __dir__)
 
 	spec.required_ruby_version = ">= 3.2"
+	spec.required_ruby_engine = "ruby"
 
 	spec.add_dependency "console", "~> 1.29"
 	spec.add_dependency "fiber-annotation"

lib/async/scheduler.rb

@@ -347,7 +347,7 @@ def io_read(io, buffer, length, offset = 0)
 				timer&.cancel!
 			end
 
-			if RUBY_ENGINE != "ruby" || RUBY_VERSION >= "3.3.1"
+			if RUBY_VERSION >= "3.3.1"
 				# Write the specified buffer to the IO.
 				#
 				# @public Since *Async v2* and *Ruby v3.3.1* with `IO::Buffer` support.