Bump serde from 1.0.215 to 1.0.216 #2240

Job	Run time
check	51s
clippy	58s
integration-test-althea-payment	12m 28s
integration-test-five-nodes	7m 58s
audit	9s
rustfmt	7s
test	4m 37s
integration-test-eth-payments	11m 48s
integration-test-debts	7m 55s
integration-test-multi-exit	10m 6s
integration-test-validate-contract	7m 30s
cross-aarch64	1m 58s
cross-armv7	2m 4s
	1h 8m 29s

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