Eliminate warnings about ambiguousness of operator

This commit removes the following Ruby warning:
    warning: `*' interpreted as argument

Enforce Lint/AmbiguousOperator again.

lib/gitlab/git/commit.rb

@@ -18,7 +18,7 @@ module Gitlab
         :committed_date, :committer_name, :committer_email
       ].freeze
 
-      attr_accessor *SERIALIZE_KEYS # rubocop:disable Lint/AmbiguousOperator
+      attr_accessor(*SERIALIZE_KEYS)
 
       def ==(other)
         return false unless other.is_a?(Gitlab::Git::Commit)

lib/gitlab/git/tag.rb

@@ -10,7 +10,7 @@ module Gitlab
       MAX_TAG_MESSAGE_DISPLAY_SIZE = 10.megabytes
       SERIALIZE_KEYS = %i[name target target_commit message].freeze
 
-      attr_accessor *SERIALIZE_KEYS # rubocop:disable Lint/AmbiguousOperator
+      attr_accessor(*SERIALIZE_KEYS)
 
       class << self
         def get_message(repository, tag_id)