Merge branch '18924-gitlab-ce-tags-page-is-not-working-502-read-timeout' into 'master'

Use memorized tags array when searching tags by name

See merge request !4859
(cherry picked from commit 9d0ef60d)

app/models/repository.rb

@@ -130,7 +130,7 @@ def find_branch(name)
   end
 
   def find_tag(name)
-    raw_repository.tags.find { |tag| tag.name == name }
+    tags.find { |tag| tag.name == name }
   end
 
   def add_branch(user, branch_name, target)