Define negated matcher properly

Co-authored-by: Phil Pirozhkov <[email protected]>

Author: ka8725

spec/rspec/rails/matchers/send_email_spec.rb

@@ -119,12 +119,7 @@ def test_email
   end
 
   context "with a custom negated version defined" do
-    around do |example|
-      RSpec::Matchers.define_negated_matcher :not_send_email, :send_email
-      example.run
-    ensure
-      undef not_send_email
-    end
+    define_negated_matcher :not_send_email, :send_email
 
     it "works with a negated version" do
       expect {