release: cut the v21.0.0-rc.6 release #2469

Job	Run time
list	23s
workflow (devkit-core-tests)	1m 27s
workflow (build-unit-tests)	2m 16s
workflow (modules-builder-tests)	1m 48s
workflow (build-cli)	1m 51s
workflow (devkit-core-tests-rerun)	1m 19s
	9m 4s

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