Call the right hooks in Repository#add_tag

This ensures Repository#add_tag calls Repository#before_push_tag instead
of just 1 random cache expiration method.

app/models/repository.rb

@@ -138,7 +138,7 @@ class Repository
   end
   def add_tag(tag_name, ref, message = nil)
-    expire_tags_cache
+    before_push_tag
     gitlab_shell.add_tag(path_with_namespace, tag_name, ref, message)
   end
@@ -334,6 +334,7 @@ class Repository
   # Runs code before pushing (= creating or removing) a tag.
   def before_push_tag
     expire_cache
+    expire_tags_cache
     expire_tag_count_cache
   end

spec/models/repository_spec.rb

@@ -649,6 +649,17 @@ describe Repository, models: true do
     end
   end
+  describe '#add_tag' do
+    it 'adds a tag' do
+      expect(repository).to receive(:before_push_tag)
+
+      expect_any_instance_of(Gitlab::Shell).to receive(:add_tag).
+        with(repository.path_with_namespace, '8.5', 'master', 'foo')
+
+      repository.add_tag('8.5', 'master', 'foo')
+    end
+  end
+
   describe '#rm_branch' do
     let(:user) { create(:user) }