C++20 allows ranges to have lvalue-qualified begin() and end() member functions. fmt correctly handles this if begin() and end() are additionally const-qualifed (i.e. begin() const&), but not in the non-const case. For example:
https://godbolt.org/z/YfxaYz5r7
This patch fixes fmt's range detection to handle this case by testing calls to detail::ranges_begin()/end() with an lvalue T&, matching the behaviour in the const case.
2595bf57b3