Remove double forward

[sylveon]

This fixes the code analysis warnings pointed out by @dmachaj. We can't just really switch to using Args const&... because some types cannot be formatted as const lvalues - most notably ranges::filter_view. So instead, we take a forwarding reference, but don't actually call std::forward, resulting in all the arguments being passed to std::format as lvalue references.

Formatters that care about the exact value category should feel bad.

[dmachaj]

Looks like this change introduced some build breaks in the cpp20 test code :(

[sylveon]

Yeah, should've actually tested it haha. Lemme fix that.

[sylveon]

Should work now :)