[YARP] Suppress constant redefinition warning

```
<compiled>:1: warning: already initialized constant Bar
test/yarp/compiler_test.rb:139: warning: previous definition of Bar was here
```

test/yarp/compiler_test.rb

@@ -134,19 +134,25 @@ module YARP
     end
 
     def test_ConstantPathTargetNode
+      verbose = $VERBOSE
       # Create some temporary nested constants
       Object.send(:const_set, "MyFoo", Object)
       Object.const_get("MyFoo").send(:const_set, "Bar", Object)
 
       constant_names = ["MyBar", "MyFoo::Bar", "MyFoo::Bar::Baz"]
       source = "#{constant_names.join(",")} = Object"
-      yarp_eval = RubyVM::InstructionSequence.compile_yarp(source).eval
+      iseq = RubyVM::InstructionSequence.compile_yarp(source)
+      $VERBOSE = nil
+      yarp_eval = iseq.eval
+      $VERBOSE = verbose
       assert_equal yarp_eval, Object
 
+    ensure
       ## Teardown temp constants
       Object.const_get("MyFoo").send(:remove_const, "Bar")
       Object.send(:remove_const, "MyFoo")
       Object.send(:remove_const, "MyBar")
+      $VERBOSE = verbose
     end
 
     def test_ConstantPathWriteNode