Exclude directory if some relative file is present in the filesystem

Sometimes it is reasonable to exclude directory, but only if some file is present.

### Example

Rust projects are defined by `Cargo.toml` file. All build files are placed to `target` directory in the project structure.
```
(project root)
|- Cargo.toml
|- src (contains source files)
| |- ...
|- target (contains build files generated by Rust tooling)
| |- ...
|- ...
```

We would like to exclude `target` directory only if the directory containing `target` directory contains also `Cargo.toml`.
In ZSH syntax it would be: `**/target(e:'[[ -f $REPLY/../Cargo.toml ]]':)`

Is it possible in Borg now?