Three more DRY spec refactors (casa_cases_spec.rb, reports_spec.rb, new_spec.rb)

[alanparmenter]

shared_examples for volunteer, supervisor and admin user roles

What github issue is this PR for, if any?

Relates to #6874

What changed, and why?

shared_examples added because these specs (casa_cases_spec.rb, reports_spec.rb, new_spec.rb) have repeated examples.

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

bundle exec rspec spec/requests/casa_cases_spec.rb
bundle exec rspec spec/requests/reports_spec.rb
bundle exec rspec spec/system/supervisors/new_spec.rb

Feelings gif (optional)