Reference "ci.skip" as constant

app/models/repository.rb

@@ -1068,7 +1068,7 @@ class Repository
     end
 
     push_options = []
-    push_options << 'ci.skip' if skip_ci
+    push_options << Gitlab::PushOptions::CI_SKIP if skip_ci
 
     raw.rebase(
       user,

lib/gitlab/push_options.rb

@@ -32,6 +32,8 @@ module Gitlab
 
     OPTION_MATCHER = /(?<namespace>[^\.]+)\.(?<key>[^=]+)=?(?<value>.*)/.freeze
 
+    CI_SKIP = 'ci.skip'
+
     attr_reader :options
 
     def initialize(options = [])