[ruby/psych] Fix symabolize_name with non-string keys

https://github.com/ruby/psych/commit/1c5c29e81f

ext/psych/lib/psych/visitors/to_ruby.rb

@@ -366,7 +366,7 @@ module Psych
               hash[key] = val
             end
           else
-            if !tagged && @symbolize_names
+            if !tagged && @symbolize_names && key.is_a?(String)
               key = key.to_sym
             elsif !@freeze
               key = deduplicate(key)

test/psych/test_psych.rb

@@ -371,17 +371,18 @@ class TestPsych < Psych::TestCase
     yaml = <<-eoyml
 foo:
   bar: baz
+  1: 2
 hoge:
   - fuga: piyo
     eoyml
 
     result = Psych.load(yaml)
-    assert_equal result, { "foo" => { "bar" => "baz"}, "hoge" => [{ "fuga" => "piyo" }] }
+    assert_equal result, { "foo" => { "bar" => "baz", 1 => 2 }, "hoge" => [{ "fuga" => "piyo" }] }
 
     result = Psych.load(yaml, symbolize_names: true)
-    assert_equal result, { foo: { bar: "baz" }, hoge: [{ fuga: "piyo" }] }
+    assert_equal result, { foo: { bar: "baz", 1 => 2 }, hoge: [{ fuga: "piyo" }] }
 
     result = Psych.safe_load(yaml, symbolize_names: true)
-    assert_equal result, { foo: { bar: "baz" }, hoge: [{ fuga: "piyo" }] }
+    assert_equal result, { foo: { bar: "baz", 1 => 2 }, hoge: [{ fuga: "piyo" }] }
   end
 end