Bump datumaro version to 1.6.0rc1 #5992

Job	Run time
Code-Quality-Checks	3m 33s
Unit-Test-with-Python3.10	13m 14s
Unit-Test-with-Python3.8	13m 52s
Unit-Test-with-Python3.9	11m 48s
Integration-Test-py310-det / run_tests_in_tox	50m 2s
Integration-Test-py310-act / run_tests_in_tox	10m 23s
Integration-Test-py310-ano / run_tests_in_tox	11m 38s
Integration-Test-py310-all / run_tests_in_tox	11m 10s
Integration-Test-py310-cls / run_tests_in_tox	24m 8s
Integration-Test-py310-seg / run_tests_in_tox	13m 58s
Integration-Test-py310-iseg / run_tests_in_tox	39m 19s
Integration-Test-py310-visprompt / run_tests_in_tox	6m 54s
	3h 29m 59s

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