Add a '?' to the custom favicon's urls

Without the '?' at the end of the favicon url the custom favicon (i.e.
the favicons that are served through `UploadController`) are not shown
in the browser. It may have something to do with how `#send_file` /
`#send_data` set http headers. When serving the same icon file from the
public directory everything is fine.

lib/gitlab/favicon.rb

@@ -2,7 +2,7 @@ module Gitlab
   class Favicon
     class << self
       def default
-        return appearance_favicon.default.url if appearance_favicon.exists?
+        return custom_favicon_url(appearance_favicon.default.url) if appearance_favicon.exists?
         return 'favicon-yellow.ico' if Gitlab::Utils.to_boolean(ENV['CANARY'])
         return 'favicon-blue.ico' if Rails.env.development?
 
@@ -11,7 +11,7 @@ module Gitlab
 
       def status(status_name)
         if appearance_favicon.exists?
-          appearance_favicon.public_send("status_#{status_name}").url
+          custom_favicon_url(appearance_favicon.public_send("status_#{status_name}").url) # rubocop:disable GitlabSecurity/PublicSend
         else
           dir = 'ci_favicons'
           dir = File.join(dir, 'dev') if Rails.env.development?
@@ -30,6 +30,13 @@ module Gitlab
       def appearance_favicon
         appearance.favicon
       end
+
+      # Without the '?' at the end of the favicon url the custom favicon (i.e.
+      # the favicons that are served through `UploadController`) are not shown
+      # in the browser.
+      def custom_favicon_url(url)
+        "#{url}?"
+      end
     end
   end
 end

spec/lib/gitlab/favicon_spec.rb

@@ -19,7 +19,7 @@ RSpec.describe Gitlab::Favicon do
 
     it 'uses the custom favicon if a favicon appearance is present' do
       create :appearance, favicon: fixture_file_upload(Rails.root.join('spec/fixtures/dk.png'))
-      expect(described_class.default).to match %r{/uploads/-/system/appearance/favicon/\d+/default_dk.ico}
+      expect(described_class.default).to match %r{/uploads/-/system/appearance/favicon/\d+/default_dk.ico\?}
     end
   end
 
@@ -32,7 +32,7 @@ RSpec.describe Gitlab::Favicon do
 
     it 'uses the custom favicon if a favicon appearance is present' do
       create :appearance, favicon: fixture_file_upload(Rails.root.join('spec/fixtures/dk.png'))
-      expect(subject).to match(%r{/uploads/-/system/appearance/favicon/\d+/status_created_dk.ico})
+      expect(subject).to match(%r{/uploads/-/system/appearance/favicon/\d+/status_created_dk.ico\?})
     end
   end
 end