dereferencing an iterator from the right view of a bimap gives inconsisent results with using ->first and ->second

**Boost version:** 1.86
**fmt version:** 11.0
**g++ version:** Apple clang version 15.0.0 (clang-1500.3.9.4)
**OS:** macOS 14.1

**Issue:**
In the following code snippet
```
boost::bimap m;
m.insert({1, "one"});

for (auto iter = m.right.begin(); iter != m.right.end(); ++iter) {
auto [k, v] = *iter;
fmt::println("key = {}, val = {}", k, v);
fmt::println("first = {}, second = {}", iter->first, iter->second);
}
```
I'd expect the two ways to print the info regarding the order. Yet I observed
```
key = 1, val = one
first = one, second = 1
```
where apprently using structured binding gives the "wrong" result in the right view.

**Expected behavior:**
Dereferencing a right iterator should give consistent results with `->first` and `->second`. Otherwise, it leads to subtle errors to use `bimap.right` in any generic code where a map is being traversed using the structured binding, i.e. `for (auto [k, v] : generic_map)`.