Update TFRT dependency to use revision http://github.com/tensorflow/runtime/commit/421af0020dece51784cb2600295cfaf5b608beee.
Update TFRT dependency to use revision
http://github.com/tensorflow/runtime/commit/421af0020dece51784cb2600295cfaf5b608beee.

PiperOrigin-RevId: 484244084

google/tsl,google/tsl,google/tsl