integration-test: boot multiboot2_chainloader itself also via Multiboot2 #1037

Job	Run time
build (nightly) / rust	41s
build (msrv) / rust	34s
build (stable) / rust	37s
style (msrv) / rust	20s
build no_std (msrv) / rust	23s
build no_std (stable) [w/o builder] / rust	13s
build no_std (stable) / rust	13s
build no_std (stable) [Windows] / rust	2m 24s
style (stable) / rust	20s
style (nightly) / rust	26s
build no_std (nightly) / rust	24s
tests with miri (nightly) / rust	1m 22s
	7m 57s

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