mrb_read_float() converts "0.3" with a small error compared to strtod() #6182

As far as I can tell, "0.6" and "0.7" also do not have the same value as strtod().

The reason I noticed this is mruby-marshal.
However, when I do Marshal.dump/load, the respective results for 0.6 and 0.7 seem to be equal.

% bin/mirb
mirb - Embeddable Interactive Ruby Shell

> Marshal.load(Marshal.dump(0.3)) == 0.3
 => false
> Marshal.load(Marshal.dump(0.6)) == 0.6
 => true
> Marshal.load(Marshal.dump(0.7)) == 0.7
 => true