Suppress warning and stdout messages in Jupyter notebooks #2422

Job	Run time
link_checker	6s
static_checks	38s
build_and_test_py_standalone	2m 3s
build_and_test_nest_desktop (master)	11m 8s
build_and_test_nest_compartmental (master)	18m 41s
build_and_test_nest (v2.20.2)	28m 6s
build_and_test_nest (v3.0)	22m 17s
build_and_test_nest (v3.8)	23m 21s
build_and_test_nest (master)	59m 40s
	2h 46m 0s

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