Misleading doc comment for std.bit_set.ArrayBitSet

[AndrewKraevskii]

https://github.com/ziglang/zig/blob/f1eed99f3d2d355054c6cf36d6f332d83b2ec595/lib/std/bit_set.zig#L315-L318 Comment says it is backed by array of usize but in fact it is backed by array of MaskIntType as can be seen here https://github.com/ziglang/zig/blob/f1eed99f3d2d355054c6cf36d6f332d83b2ec595/lib/std/bit_set.zig#L378-L380 It also repeated here https://github.com/ziglang/zig/blob/f1eed99f3d2d355054c6cf36d6f332d83b2ec595/lib/std/bit_set.zig#L17