[ruby/psych] Bump version to 5.1 for release

This version primarily updates the JRuby extension to use
SnakeYAML Engine, a newer version of the SnakeYAML library, which
also updates YAML support to 1.2. The JRuby extension now also
exposes settings for the parser.

https://github.com/ruby/psych/commit/6f2b16b343

ext/psych/lib/psych/versions.rb

@@ -2,7 +2,7 @@
 
 module Psych
   # The version of Psych you are using
-  VERSION = '5.0.2'
+  VERSION = '5.1.0'
 
   if RUBY_ENGINE == 'jruby'
     DEFAULT_SNAKEYAML_VERSION = '2.6'.freeze