ci: bring back bare metal OS builds #285

Job	Run time
clippy	28s
test (1.85.0)	37s
cross (powerpc-unknown-linux-gnu, stable)	1m 8s
cross (powerpc-unknown-linux-gnu, 1.85.0)	1m 5s
doc	29s
rustfmt	15s
no_std (stable, thumbv7em-none-eabi)	36s
test (stable)	37s
no_std (1.85.0, thumbv7em-none-eabi)	37s
no_std (1.85.0, armv7a-none-eabi)	36s
no_std (stable, armv7a-none-eabi)	38s
no_std (stable, wasm32-unknown-unknown)	47s
no_std (1.85.0, wasm32-unknown-unknown)	43s
	8m 36s

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