Rust

Use CSS class `markdown-alert` instead of `alert` #1201

Job	Run time
build_lib_test (nightly)	50s
build_bin_spec (nightly)	1m 3s
build_lib_test (beta)	1m 0s
build_wasm (nightly)	44s
build_bin_spec (beta)	59s
build_lib_test (stable)	55s
build_wasm (beta)	46s
build_bin_spec (stable)	53s
build_lib_test ($MSRV)	2m 55s
build_wasm (stable)	46s
build_bin_spec ($MSRV)	2m 48s
build_wasm ($MSRV)	2m 34s
clippy_format	2m 24s
lockfile	57s
no_features_build_test (nightly)	24s
no_features_build_test (beta)	25s
no_features_build_test (stable)	18s
no_features_build_test ($MSRV)	2m 6s
	22m 47s

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