craterbot: error with documented crate selection format

[lqd]

Opening an issue as requested by @Mark-Simulacrum :

While launching a run on a limited selection of crates on this PR using the crates=list:link format documented here, the bot returned a "missing desired crates" error.

Note that using the (apparently undocumented ?) crates=link format worked fine, so I'm not sure if this is the only accepted format or if the documented format is not available in all comments shorthands, or if it's something else.