Update all upload/download-artifact uses to v4 #1689

Job	Run time
validate_imported_protos / Validate Imported Proto Files	16s
validate_python / Validate Python Code	1m 29s
cancel_builds / Cancel Build(s)	3s
create_client_artifacts / Windows Artifacts	49s
create_client_artifacts / Linux Artifacts	14s
build_desktop / Windows Build	1h 35m 22s
build_nilrt / NILRT Cross Compile with GCC 6.3.0	41m 32s
build_desktop / Ubuntu Build	1h 0m 21s
create_release	0s
run_ubuntu_system_tests / Run Tests	1m 31s
run_win_system_tests / Run Tests	26s
	3h 22m 3s

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