Release 2.21: Update copyright year #624

Job	Run time
build (asan, -DANALYZE_ADDRESS=On, true, process, false)	13m 42s
build (ubsan, -DANALYZE_UNDEFINED=On, true, process, true)	24m 52s
build (tsan, -DANALYZE_THREAD=On, false, thread, false, --executor=thread --error-exitcode=0)	9m 41s
	48m 15s

Provide feedback