Add missing require 'pp'

When using `PP.pp` you still have to `require 'pp'`.

Fixes `uninitialized constant RSpec::LintExampleGroup::HaveProblem::PP`

Also see related discussion in
rubocop/rubocop#11099 (comment)

Author: alexjfisher

spec/spec_helper.rb

@@ -22,6 +22,7 @@
 
 require 'puppet-lint'
 require 'rspec/its'
+require 'pp'
 begin
   require 'rspec/json_expectations'
 rescue LoadError, SyntaxError