Rust

Use CSS class `markdown-alert` instead of `alert` #1198

Job	Run time
build_lib_test (nightly)	55s
build_bin_spec (nightly)	1m 5s
build_lib_test (beta)	1m 4s
lockfile	56s
build_bin_spec (beta)	1m 7s
build_lib_test (stable)	1m 5s
build_wasm (nightly)	47s
build_bin_spec (stable)	1m 2s
build_wasm (beta)	47s
build_lib_test ($MSRV)	2m 56s
build_bin_spec ($MSRV)	1m 17s
build_wasm (stable)	44s
no_features_build_test (nightly)	30s
build_wasm ($MSRV)	2m 36s
no_features_build_test (beta)	30s
clippy_format	2m 16s
no_features_build_test (stable)	18s
no_features_build_test ($MSRV)	2m 2s
	21m 57s

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