Dont use cached collection for Repository find_branch and find_tag methods

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

CHANGELOG

@@ -14,6 +14,7 @@ v 8.3.0 (unreleased)
   - Expose events API with comment information and author info
   - Fix: Ensure "Remove Source Branch" button is not shown when branch is being deleted. #3583
   - Run custom Git hooks when branch is created or deleted.
+  - Fix bug when simultaneously accepting multiple MRs results in MRs that are of "merged" status, but not merged to the target branch
 v 8.2.3
   - Fix application settings cache not expiring after changes (Stan Hu)

app/models/repository.rb

@@ -100,11 +100,11 @@ class Repository
   end
   def find_branch(name)
-    branches.find { |branch| branch.name == name }
+    raw_repository.branches.find { |branch| branch.name == name }
   end
   def find_tag(name)
-    tags.find { |tag| tag.name == name }
+    raw_repository.tags.find { |tag| tag.name == name }
   end
   def add_branch(user, branch_name, target)