Release 2.21: Update copyright year #623

Job	Run time
build (tsan, -DANALYZE_THREAD=On, false, thread, false, --executor=thread --error-exitcode=0)	10m 30s
build (asan, -DANALYZE_ADDRESS=On, true, process, false)	12m 52s
build (ubsan, -DANALYZE_UNDEFINED=On, true, process, true)	26m 14s
	49m 36s

Provide feedback