Update System.Memory to 4.6.3 #13043

Job	Run time
setup-environment	1m 24s
generate-metrics	5m 41s
gofmt	7m 7s
coverage	11m 51s
cross-compile (binaries-darwin_amd64)	5m 20s
lint	11m 49s
cross-compile (binaries-darwin_arm64)	5m 12s
test	16m 48s
cross-compile (binaries-linux_amd64)	5m 5s
cross-compile (binaries-linux_arm64)	5m 10s
tidy	2m 25s
cross-compile (binaries-windows_amd64)	5m 8s
cross-compile (binaries-linux_ppc64le)	5m 9s
	1h 28m 9s

Provide feedback