tidy error: rustc-perf workspace doesn't have a Cargo.lock

Tidy check (`x test tidy`) currently fails with

```
tidy error: the `src/tools/rustc-perf` workspace doesn't have a Cargo.lock
```

If you don't have `rustc-perf` submodule initialized.

### Temporary workaround

```bash
git submodule update --init --recursive
```