Another three DRY spec refactors (case_contacts_helper_spec.rb, resolve_spec.rb, header.html.erb_spec.rb)

[alanparmenter]

What github issue is this PR for, if any?

Relates to #6874

What changed, and why?

shared_examples added because these specs (case_contacts_helper_spec.rb, resolve_spec.rb, header.html.erb_spec.rb) have repeated examples.

How is this tested? (please write rspec and jest tests!) 💖💪

bundle exec rspec spec/helpers/case_contacts_helper_spec.rb
bundle exec rspec spec/system/case_contacts/followups/resolve_spec.rb
bundle exec rspec spec/views/layouts/header.html.erb_spec.rb

Feelings gif (optional)