Bump marshmallow from 3.20.1 to 3.21.3 #797

Job	Run time
lint	35s
integration (tests-noqueue, QuickTest)	1m 37s
unit (utests)	1m 8s
unit (tests-api-mock)	1m 1s
integration (tests-noqueue, BuildFailedTest)	44s
integration (tests-noqueue, RepositoryTests)	32s
unit (tests-server)	57s
integration (tests-noqueue, TestBertE)	5m 54s
integration (tests-noqueue, TestQueueing)	31s
integration (tests-noqueue, TaskQueueTests)	3m 27s
integration (tests, QuickTest)	1m 37s
integration (tests, BuildFailedTest)	33s
integration (tests, RepositoryTests)	33s
integration (tests, TestBertE)	7m 10s
integration (tests, TestQueueing)	5m 30s
integration (tests, TaskQueueTests)	3m 27s
	35m 16s

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