Use stable rustfmt #5867

Job	Run time
format	32s
cargo (ubuntu-latest)	22s
bare-metal (src/bare-metal/alloc-example, aarch64-unknown-none)	23s
cargo (macos-latest)	25s
find-languages	6s
bare-metal (src/bare-metal/aps/examples, aarch64-unknown-none)	25s
typos	5s
bare-metal (src/bare-metal/microcontrollers/examples, thumbv7em-none-eabihf)	44s
bare-metal (src/exercises/bare-metal/compass, thumbv7em-none-eabihf)	1m 26s
bare-metal (src/exercises/bare-metal/rtc, aarch64-unknown-none)	23s
build (bn)	3m 37s
build (da)	3m 49s
build (de)	3m 19s
build (el)	3m 37s
build (en)	3m 18s
build (es)	3m 36s
build (fa)	3m 59s
build (fr)	3m 17s
build (id)	3m 17s
build (it)	3m 24s
build (ja)	4m 31s
build (ko)	4m 37s
build (pl)	3m 41s
build (pt-BR)	3m 18s
build (ro)	3m 18s
build (ru)	3m 41s
build (tr)	3m 6s
build (uk)	3m 37s
build (vi)	3m 8s
build (zh-CN)	4m 0s
build (zh-TW)	4m 13s
	1h 21m 14s

Provide feedback