Ambiguous partial specialization when formatting boost flat_set since fmt v10.0.0

[5chmidti]

When trying to format a flat_set from boost, an ambiguous lookup for formatter happens.

Reproducer:
https://godbolt.org/z/dhqnMf755
boost version 1.82.0 (changing it to some random previous versions did not change something)
Clang 16.0.0 with fmt trunk
gcc 13.2 with fmt trunk
gcc 13.2 with fmt 9.1.0 as a proof it worked with fmt 9.1.0

The ambiguous formatters are in lines

fmt/include/fmt/ranges.h

Line 560 in 757564f

struct formatter<

and

fmt/include/fmt/ranges.h

Line 671 in 757564f

struct formatter<T, Char,

[vitaut]

I think we should add range_format_kind<R, Char>::value == range_format::disabled in the second specialization. A PR is welcome.