Ensure Time.parse returns UTC for consistency with Numeric path

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: jnunemaker

lib/flipper/expressions/time.rb

@@ -8,7 +8,7 @@ def self.call(value)
         when Numeric
           ::Time.at(value).utc
         else
-          ::Time.parse(value)
+          ::Time.parse(value).utc
         end
       end
     end