[Rails5] Set request.format for artifacts_controller

Since Rails 5 request.format gets set by extension if it's not explicitly
set.
That means artifacts_controller#file no longer works as expected.
This commit explicitly sets request.format for artifacts_controller#file.

app/controllers/projects/artifacts_controller.rb

@@ -7,6 +7,7 @@ class Projects::ArtifactsController < Projects::ApplicationController
   before_action :authorize_read_build!
   before_action :authorize_update_build!, only: [:keep]
   before_action :extract_ref_name_and_path
+  before_action :set_request_format, only: [:file]
   before_action :validate_artifacts!
   before_action :entry, only: [:file]
 
@@ -101,4 +102,12 @@ class Projects::ArtifactsController < Projects::ApplicationController
 
     render_404 unless @entry.exists?
   end
+
+  def set_request_format
+    request.format = :html if set_request_format?
+  end
+
+  def set_request_format?
+    request.format != :json
+  end
 end

changelogs/unreleased/blackst0ne-rails5-expected-the-response-to-have-status-code-ok-but-it-was-404.yml

+---
+title: "[Rails5] Set request.format for artifacts_controller"
+merge_request: 19937
+author: "@blackst0ne"
+type: fixed