Resolve "[Rails5] `ActionView::MissingTemplate` in spec/features/projects/wiki/user_views_wiki_page_spec.rb"

What does this MR do?

In rails 4 the route default parameter falls to text/html if its value is nil.
In rails 5 it doesn't act like that anymore.

See https://github.com/rails/rails/issues/28901 and https://github.com/rails/rails/pull/20831

In this MR an explicit format value was added to act like rails 4.

Fixes rails5 errors:

  1) User views a wiki page when Gitaly is enabled behaves like wiki page user view when a page does not have history shows the creation page if file does not exist
     Failure/Error: render 'edit'

     ActionView::MissingTemplate:
       Missing template projects/wikis/edit, projects/application/edit, application/edit with {:locale=>[:en], :formats=>[:jpeg], :variants=>[], :handlers=>[:raw, :erb, :html, :builder, :ruby, :haml]}. Searched in:
         * "/builds/gitlab-org/gitlab-ce/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/peek-sidekiq-1.0.3/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/peek-redis-1.2.0/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/peek-rblineprof-0.2.0/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/peek-gc-0.0.2/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/peek-1.0.1/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/kaminari-core-1.0.1/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/graphiql-rails-1.4.10/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/doorkeeper-4.3.2/app/views"
         * "/builds/gitlab-org/gitlab-ce/vendor/ruby/2.4.0/gems/devise-4.4.3/app/views"
     Shared Example Group: "wiki page user view" called from ./spec/features/projects/wiki/user_views_wiki_page_spec.rb:151
     # ./app/controllers/projects/wikis_controller.rb:34:in `show'
     # ./lib/gitlab/i18n.rb:50:in `with_locale'
     # ./lib/gitlab/i18n.rb:56:in `with_user_locale'
     # ./app/controllers/application_controller.rb:360:in `set_locale'
     # ./lib/gitlab/middleware/multipart.rb:95:in `call'
     # ./lib/gitlab/request_profiler/middleware.rb:14:in `call'
     # ./lib/gitlab/query_limiting/middleware.rb:17:in `block in call'
     # ./lib/gitlab/query_limiting/transaction.rb:37:in `run'
     # ./lib/gitlab/query_limiting/middleware.rb:16:in `call'
     # ./lib/gitlab/middleware/go.rb:17:in `call'
     # ./lib/gitlab/etag_caching/middleware.rb:11:in `call'
     # ./lib/gitlab/middleware/read_only/controller.rb:28:in `call'
     # ./lib/gitlab/middleware/read_only.rb:16:in `call'
     # ./lib/gitlab/request_context.rb:18:in `call'
     # ./config/initializers/fix_local_cache_middleware.rb:9:in `call'
     # ./lib/gitlab/middleware/static.rb:9:in `call'
     # ./lib/gitlab/testing/request_inspector_middleware.rb:31:in `call'
     # ./lib/gitlab/testing/request_blocker_middleware.rb:45:in `call'
     # ./lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
     # ./spec/features/projects/wiki/user_views_wiki_page_spec.rb:108:in `block (4 levels) in <top (required)>'

Are there points in the code the reviewer needs to double check?

No.

Why was this MR needed?

Migration to Rails 5.0

Screenshots (if relevant)

No.

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Closes #47738 (closed)