Fix a Grape deprecation, use `#request_method` instead of `#route_method`

changelogs/unreleased/fix-api-deprecation.yml

+---
+title: Fix a Grape deprecation, use `#request_method` instead of `#route_method`
+merge_request:
+author:

lib/api/helpers.rb

@@ -96,7 +96,7 @@ module API
     end
 
     def authenticate_non_get!
-      authenticate! unless %w[GET HEAD].include?(route.route_method)
+      authenticate! unless %w[GET HEAD].include?(route.request_method)
     end
 
     def authenticate_by_gitlab_shell_token!

spec/requests/api/helpers_spec.rb

@@ -396,7 +396,7 @@ describe API::Helpers, api: true do
     %w[HEAD GET].each do |method_name|
       context "method is #{method_name}" do
         before do
-          expect_any_instance_of(self.class).to receive(:route).and_return(double(route_method: method_name))
+          expect_any_instance_of(self.class).to receive(:route).and_return(double(request_method: method_name))
         end
 
         it 'does not raise an error' do
@@ -410,7 +410,7 @@ describe API::Helpers, api: true do
     %w[POST PUT PATCH DELETE].each do |method_name|
       context "method is #{method_name}" do
         before do
-          expect_any_instance_of(self.class).to receive(:route).and_return(double(route_method: method_name))
+          expect_any_instance_of(self.class).to receive(:route).and_return(double(request_method: method_name))
         end
 
         it 'calls authenticate!' do