[clang-tidy] False-positive result of check readability-redundant-parentheses with rvalue overload

This code triggers a false-positive result from clang-tidy check readability-redundant-parentheses (see https://godbolt.org/z/bME79eef6):
```c++
#include
#include

std::string getString()
{
return (std::ostringstream{} << "Hello World").str(); // <-- this line triggers the warning
}

int main()
{
std::cout << getString() << '\n';
return 0;
}
```

The issue occurs on the main branch (upcoming clang 23). In clang 22 there was no such warning.

Start by reproducing the warning with the C++ example and Godbolt link, then inspect the clang-tidy readability-redundant-parentheses check. Done means the shown rvalue-overload expression no longer produces a false positive and a regression test covers the case.

Written by the indexing model from the issue text.