Remove warnings in test suite

lib/active_record/store.rb:79: warning: method redefined; discarding old color=
lib/active_record/store.rb:79: warning: previous definition of color= was here
lib/active_record/store.rb:83: warning: method redefined; discarding old color
lib/active_record/store.rb:83: warning: previous definition of color was here
Merge pull request #13616 from zirni/remove_warnings

Remove warnings in test suite