By looking only for file descriptors pointing to the current test
directory (i.e. exclude the internal file descriptors of Node).

And forward stdin/stderr to `/dev/null`, we are only interested
in `stdout`.

So:
```
find /proc/<PROCESS>/fd -lname "<DIR>*" -printf "%l\n" || true
```

Instead of:
```
find /proc/<PROCESS>/fd -lname "<DIR>*" -printf "%l
" || true
```

Fixes: #16887.