(maint) Add note to update the puppetlabs_spec_helper lint whenever it is change here

In order to ensure that our lint testing remains in step we must keep these two files in sync with eachother:
- https://github.com/puppetlabs/puppetlabs_spec_helper/blob/main/lib/puppetlabs_spec_helper/rake_tasks.rb#L124
- https://github.com/puppetlabs/pdk-templates/blob/d9e6478ff7730a8ce072ce0c1d36a9b79f05ba2c/config_defaults.yml#L69