Enable (and disable) more rubocops

app/models/ci/build.rb

@@ -23,7 +23,7 @@ def persisted_environment
     serialize :yaml_variables, Gitlab::Serializer::Ci::Variables
 
     validates :coverage, numericality: true, allow_blank: true
-    validates_presence_of :ref
+    validates :ref, presence: true
 
     scope :unstarted, ->() { where(runner_id: nil) }
     scope :ignore_failures, ->() { where(allow_failure: false) }