matrix: remove bold printing of diagonal elements #22494

Job	Run time
build (check_format)	1m 1s
build (tests)	5m 38s
build (tests_coverage)	6m 28s
build (px4_fmu-v2_default stack_check)	3m 16s
build (validate_module_configs)	50s
build (shellcheck_all)	1m 34s
build (NO_NINJA_BUILD=1 px4_fmu-v5_default)	4m 5s
build (NO_NINJA_BUILD=1 px4_sitl_default)	3m 14s
build (airframe_metadata)	1m 2s
build (module_documentation)	1m 4s
build (parameters_metadata)	1m 9s
	29m 21s

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