Change test case name to FormatValidationTest

I believe that this was caused by a copy/paste mistake.

activemodel/test/cases/validations/format_validation_test.rb

@@ -5,7 +5,7 @@
 require "models/topic"
 require "models/person"
 
-class PresenceValidationTest < ActiveModel::TestCase
+class FormatValidationTest < ActiveModel::TestCase
   def teardown
     Topic.clear_validators!
   end