test/ruby/test_iseq.rb: Prevent a warning

http://rubyci.s3.amazonaws.com/ubuntu/ruby-master/log/20211109T063003Z.log.html.gz
```
[ 9898/21145] TestISeq#test_super_with_block_and_kwrest/home/chkbuild/chkbuild/tmp/build/20211109T063003Z/ruby/test/ruby/test_iseq.rb:1: warning: method redefined; discarding old touch
/home/chkbuild/chkbuild/tmp/build/20211109T063003Z/ruby/test/ruby/test_iseq.rb:1: warning: previous definition of touch was here
 = 0.00 s
```

test/ruby/test_iseq.rb

@@ -107,7 +107,7 @@ def touch(*) # :nodoc:
 
   def test_super_with_block_and_kwrest
     iseq = compile(<<~EOF)
-      def touch(**) # :nodoc:
+      def touch2(**) # :nodoc:
         foo { super }
       end
       42