添加github workflow，检查代码是否已经格式化 #7

	name: Rust format check

	on: [push, pull_request]

	jobs:
	# ensure the toolchain is cached
	ensure-toolchain:
	uses: ./.github/workflows/cache-toolchain.yml

	fmt:
	name: check
	runs-on: ubuntu-latest
	needs: [ensure-toolchain]
	steps:
	- uses: actions/checkout@v3

	# 准备 bindings.rs
	# 由于 bindings.rs 是在 build.rs 中生成的，而这里为了方便，直接 touch 一个空文件
	- name: prepare bindings
	run: \|
	printf "\n" >> kernel/src/include/bindings/bindings.rs
	printf "\n" >> user/libs/libc/src/include/internal/bindings/bindings.rs

	- name: Install rustfmt
	run: rustup component add rustfmt

	- name: Check format
	uses: actions-rs/cargo@v1
	with:
	command: fmt
	args: --all -- --check

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