[clang-tidy] don't warn when returning the result for bugprone-standalone-empty

Relevant issue: https://github.com/llvm/llvm-project/issues/59517

Currently this check will warn when the result is used in a `return`
statement, e.g.

```
bool foobar() {
  std::vector<int> v;
  return v.empty();
  // will get a warning here, which makes no sense IMO
}
```

Reviewed By: cjdb, denik

Differential Revision: https://reviews.llvm.org/D141107