ci: bring back bare metal OS builds #292

Job	Run time
doc	33s
no_std (stable, wasm32-unknown-unknown)	45s
no_std (1.85.0, wasm32-unknown-unknown)	40s
no_std (stable, armv7a-none-eabi)	44s
cross (powerpc-unknown-linux-gnu, stable)	1m 13s
cross (powerpc-unknown-linux-gnu, 1.85.0)	1m 6s
test (stable)	37s
no_std (1.85.0, armv7a-none-eabi)	41s
clippy	28s
no_std (stable, thumbv7em-none-eabi)	50s
no_std (1.85.0, thumbv7em-none-eabi)	42s
rustfmt	12s
test (1.85.0)	41s
	9m 12s

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