{ext,test}/etc: Specify frozen_string_literal: true.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57451 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/etc/extconf.rb

@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require 'mkmf'
 
 headers = []

ext/etc/mkconstants.rb

@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require 'optparse'
 require 'erb'
 

test/etc/test_etc.rb

@@ -1,4 +1,4 @@
-# frozen_string_literal: false
+# frozen_string_literal: true
 require "test/unit"
 require "etc"