Update the directory for unshifting

Path of file changed in https://gitlab.com/gitlab-org/gitlab/merge_requests/23335 but reference to directory did not
Closes https://gitlab.com/gitlab-org/gitlab/issues/198274

scripts/flaky_examples/prune-old-flaky-examples

@@ -7,7 +7,7 @@ require 'rubygems'
 
 # In newer Ruby, alias_method is not private then we don't need __send__
 singleton_class.__send__(:alias_method, :require_dependency, :require) # rubocop:disable GitlabSecurity/PublicSend
-$:.unshift(File.expand_path('../lib', __dir__))
+$:.unshift(File.expand_path('../../lib', __dir__))
 
 require 'rspec_flaky/report'