Set const_get in Simplifiable to not inherit scope

Also fix specs to define the constants for the :entry class, not the
ancestor class Simplifiable

lib/gitlab/config/entry/simplifiable.rb

@@ -35,15 +35,13 @@ module Gitlab
           @strategies ||= []
         end
 
-        # rubocop:disable Cop/ConstGetInheritFalse
         def self.entry_class(strategy)
           if strategy.present?
-            self.const_get(strategy.name)
+            self.const_get(strategy.name, false)
           else
             self::UnknownStrategy
           end
         end
-        # rubocop:enable Cop/ConstGetInheritFalse
 
         def self.default
         end

spec/lib/gitlab/config/entry/simplifiable_spec.rb

@@ -24,9 +24,9 @@ describe Gitlab::Config::Entry::Simplifiable do
     let(:unknown) { double('unknown strategy') }
 
     before do
-      stub_const("#{described_class.name}::Something", first)
-      stub_const("#{described_class.name}::DifferentOne", second)
-      stub_const("#{described_class.name}::UnknownStrategy", unknown)
+      entry::Something = first
+      entry::DifferentOne = second
+      entry::UnknownStrategy = unknown
     end
 
     context 'when first strategy should be used' do