Don't use deprecated Rack::VERSION in Rack 3

lib/webmock/rack_response.rb

@@ -47,7 +47,9 @@ def build_rack_env(request)
       # Rack-specific variables
       env['rack.input']      = StringIO.new(body)
       env['rack.errors']     = $stderr
-      env['rack.version']    = Rack::VERSION
+      if !Rack.const_defined?(:RELEASE) || Rack::RELEASE < "3"
+        env['rack.version']    = Rack::VERSION
+      end
       env['rack.url_scheme'] = uri.scheme
       env['rack.run_once']   = true
       env['rack.session']    = session

spec/support/my_rack_app.rb

@@ -37,6 +37,8 @@ def self.call(env)
       when ['GET', '/error']
         env['rack.errors'].puts('Error!')
         [500, {}, ['']]
+      when ['GET', '/env']
+        [200, {}, [JSON.dump(env)]]
       else
         [404, {}, ['']]
     end

spec/unit/rack_response_spec.rb

@@ -69,6 +69,20 @@
     expect(response.body).to include('Good to meet you, Олег!')
   end
 
+  it "should send or not a rack.version depending on the Rack version" do
+    request = WebMock::RequestSignature.new(:get, 'www.example.com/env')
+    response = @rack_response.evaluate(request)
+
+    expect(response.status.first).to eq(200)
+    body = JSON.parse(response.body)
+
+    if Gem.loaded_specs["rack"].version > Gem::Version.new("3.0.0")
+      expect(body).not_to include("rack.version")
+    else
+      expect(body).to include("rack.version")
+    end
+  end
+
   describe 'rack error output' do
     before :each do
       @original_stderr = $stderr