[rubygems/rubygems] Restore ability to load old marshalled gemspec th…

…at use `YAML::PrivateType`

This issue was not detected because when all traces of old YAML parser
and emitter `Syck` were removed, this null-type.gemspec.rz marshalled
gemspec was updated to no longer load `YAML::Syck::PrivateType` but load
`Psych::PrivateType` instead.

However, realworld old marshalled gemspecs still use the
`YAML::PrivateType` constant, so this commit replaces the gemspec to be
the real pry-0.4.7 marshalled gemspec, so that it catches this issue.

rubygems/rubygems@51b330b8d2

lib/rubygems/specification.rb

@@ -1270,7 +1270,14 @@ def self.unresolved_deps
   def self._load(str)
     Gem.load_yaml
 
-    array = Marshal.load str
+    array = begin
+      Marshal.load str
+    rescue ArgumentError => e
+      raise unless e.message.include?("YAML")
+
+      Object.const_set "YAML", Psych
+      Marshal.load str
+    end
 
     spec = Gem::Specification.new
     spec.instance_variable_set :@specification_version, array[1]