Refactor #expire_caches_before_rename method

Now that there are 3 repositories being treated in the same we, we can
iterate over them to make this method more concise.

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/31165#note_338069911

app/models/project.rb

@@ -1436,20 +1436,12 @@ class Project < ApplicationRecord
 
   # Expires various caches before a project is renamed.
   def expire_caches_before_rename(old_path)
-    repo = Repository.new(old_path, self, shard: repository_storage)
-    wiki = Repository.new("#{old_path}.wiki", self, shard: repository_storage, repo_type: Gitlab::GlRepository::WIKI)
-    design = Repository.new("#{old_path}#{Gitlab::GlRepository::DESIGN.path_suffix}", self, shard: repository_storage, repo_type: Gitlab::GlRepository::DESIGN)
+    project_repo = Repository.new(old_path, self, shard: repository_storage)
+    wiki_repo = Repository.new("#{old_path}#{Gitlab::GlRepository::WIKI.path_suffix}", self, shard: repository_storage, repo_type: Gitlab::GlRepository::WIKI)
+    design_repo = Repository.new("#{old_path}#{Gitlab::GlRepository::DESIGN.path_suffix}", self, shard: repository_storage, repo_type: Gitlab::GlRepository::DESIGN)
 
-    if repo.exists?
-      repo.before_delete
-    end
-
-    if wiki.exists?
-      wiki.before_delete
-    end
-
-    if design.exists?
-      design.before_delete
+    [project_repo, wiki_repo, design_repo].each do |repo|
+      repo.before_delete if repo.exists?
     end
   end