Switch `extract-rust-action.yml` to use `sed` rather than Taplo

[BD103]

extract-rust-action.yml currently installs Taplo and uses it to parse rust-toolchain.toml. The linter action, however, uses the built-in sed command without installing anything. I think we should switch extract-rust-version.yml to use sed as well, because it will make the behavior consistent between the two and reduce CI time.