Fix specs for yield in singleton class being deprecated

* Use eval to trigger warning only when the method is called.
* Suppress warnings and clarify this will be removed in 3.0.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@67031 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

fixtures/class.rb

@@ -1,9 +1,11 @@
 module ClassSpecs
 
   def self.sclass_with_block
+    eval <<-RUBY
     class << self
       yield
     end
+    RUBY
   end
 
   def self.sclass_with_return

language/class_spec.rb

@@ -285,8 +285,12 @@ def xyz
     }.should raise_error(TypeError)
   end
 
-  it "allows accessing the block of the original scope" do
-    ClassSpecs.sclass_with_block { 123 }.should == 123
+  ruby_version_is ""..."3.0" do
+    it "allows accessing the block of the original scope" do
+      suppress_warning do
+        ClassSpecs.sclass_with_block { 123 }.should == 123
+      end
+    end
   end
 
   it "can use return to cause the enclosing method to return" do