Rename unprocessable_entity to unprocessable_content

When the 422 status was initially proposed in
[RFC4918](https://datatracker.ietf.org/doc/html/rfc4918) (2007), it was
called 'Unprocessable entity'.

When it became a standard in
[RFC9110](https://datatracker.ietf.org/doc/html/rfc9110) (2022), it was
renamed 'Unprocessable content'.

Rack now supports it as `:unprocessable_content` and has deprecated
`:unprocessable_entity`. This commit updates it to use the new name.

Author: DavidBiddle

app/controllers/forms/check_your_answers_controller.rb

@@ -26,7 +26,7 @@ def submit_answers
       unless email_confirmation_input.valid?
         setup_check_your_answers
 
-        return render template: "forms/check_your_answers/show", locals: { email_confirmation_input: }, status: :unprocessable_entity
+        return render template: "forms/check_your_answers/show", locals: { email_confirmation_input: }, status: :unprocessable_content
       end
 
       return redirect_to error_repeat_submission_path(current_form.id) if current_context.form_submitted?

app/controllers/forms/page_controller.rb

@@ -30,7 +30,7 @@ def save
         redirect_post_save
       else
         setup_instance_vars_for_view
-        render :show, status: :unprocessable_entity
+        render :show, status: :unprocessable_content
       end
     end
 
@@ -152,7 +152,7 @@ def check_goto_page_routing_error
         error_name: first_goto_error_name,
         link_url: admin_edit_condition_url(@step.form_id, routes_page_id),
         question_number: routes_page.page_number,
-      }, status: :unprocessable_entity
+      }, status: :unprocessable_content
     end
 
     def admin_edit_condition_url(form_id, page_id)

app/controllers/forms/remove_answer_controller.rb

@@ -8,7 +8,7 @@ def delete
       @remove_input = RemoveInput.new(remove_input_params)
 
       if @remove_input.invalid?
-        return render :show, status: :unprocessable_entity
+        return render :show, status: :unprocessable_content
       end
 
       if @remove_input.remove?

app/controllers/forms/remove_file_controller.rb

@@ -12,7 +12,7 @@ def destroy
 
       if @remove_input.invalid?
         setup_urls
-        return render :show, status: :unprocessable_entity
+        return render :show, status: :unprocessable_content
       end
 
       if @remove_input.remove?

spec/requests/forms/check_your_answers_controller_spec.rb

@@ -558,7 +558,7 @@
       end
 
       it "return 422 error code" do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it "renders the check your answers page" do
@@ -584,7 +584,7 @@
       end
 
       it "return 422 error code" do
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
 
       it "renders the check your answers page" do

spec/requests/forms/page_controller_spec.rb

@@ -284,7 +284,7 @@
 
         it "returns a 422 response" do
           get form_page_path(mode:, form_id: 2, form_slug: form_data.form_slug, page_slug: 1)
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
 
         it "shows the error page" do
@@ -313,7 +313,7 @@
 
           it "returns a 422 response" do
             get form_page_path(mode:, form_id: 2, form_slug: form_data.form_slug, page_slug: 4)
-            expect(response).to have_http_status(:unprocessable_entity)
+            expect(response).to have_http_status(:unprocessable_content)
           end
 
           it "shows the error page" do
@@ -331,7 +331,7 @@
 
         it "returns a 422 response" do
           get form_page_path(mode:, form_id: 2, form_slug: form_data.form_slug, page_slug: 1)
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
 
         it "shows the error page" do
@@ -426,7 +426,7 @@
         end
 
         it "returns 422" do
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
 
         it "adds validation_errors logging attribute" do
@@ -601,7 +601,7 @@
 
         it "returns a 422 response" do
           post save_form_page_path(mode:, form_id: 2, form_slug: form_data.form_slug, page_slug: 1), params: { question: { selection: "Option 2" }, changing_existing_answer: false }
-          expect(response).to have_http_status(:unprocessable_entity)
+          expect(response).to have_http_status(:unprocessable_content)
         end
 
         it "shows the error page" do

spec/requests/forms/remove_answer_controller_spec.rb

@@ -82,7 +82,7 @@
       it "renders the show template" do
         delete "/preview-draft/#{form.id}/#{form.form_slug}/#{first_step_in_form.id}/1/remove", params: { remove_input: { remove: } }
         expect(response).to render_template(:show)
-        expect(response).to have_http_status(:unprocessable_entity)
+        expect(response).to have_http_status(:unprocessable_content)
       end
     end
 

spec/requests/forms/remove_file_controller_spec.rb

@@ -130,7 +130,7 @@
 
         it "renders the remove file page with 422 status" do
           expect(response).to render_template("forms/remove_file/show")
-          expect(response).to have_http_status :unprocessable_entity
+          expect(response).to have_http_status :unprocessable_content
         end
 
         it "displays an error" do