6724: Fix `diagnostics` subcommand, look at all modules r=jonas-schievink a=jonas-schievink
The `diagnostics` subcommand used to only compute diagnostics for `lib.rs` / the root module of all workspace crates. This fixed it and makes it look at every module.
bors r+
Co-authored-by: Jonas Schievink <jonasschievink@gmail.com>