multiboot2: add missing tags #1023

Job	Run time
build (stable) / rust	15s
build (nightly) / rust	25s
build (msrv) / rust	17s
style (msrv)	0s
build no_std (msrv)	0s
build no_std (stable) [w/o builder] / rust	13s
build no_std (stable) / rust	41s
build no_std (stable) [Windows] / rust	2m 52s
style (stable) / rust	20s
style (nightly) / rust	23s
build no_std (nightly) / rust	24s
tests with miri (nightly) / rust	1m 41s
	7m 31s

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