Auto merge of #4292 - xftroxgpx:unconfuse_bin_name, r=matklad

Auto merge of #4292 - xftroxgpx:unconfuse_bin_name, r=matklad

quote the binary name in the warning

to avoid confusion when the warning happens inside a workspace, example:
pwd is rustlearnage/rust_books/1_first_edition/closures/
and `cargo run` shows:
```
warning: path `src/main.rs` was erroneously implicitly accepted for binary match,
please set bin.path in Cargo.toml
```
(note that 'match' is not quoted, so it's confusing)

the 'match' project that it's referring to is in rustlearnage/rust_books/1_first_edition/match/
(note: Cargo.toml [workspace] is in rustlearnage/ )