Add explicit tests for from_str_radix with negative inputs to unsigned destinations and for inputs with underscores in them

Author: Krappa322

library/core/tests/num/int_macros.rs

@@ -246,6 +246,8 @@ macro_rules! int_module {
 
                 assert_eq!($T::from_str_radix("Z", 35).ok(), None::<$T>);
                 assert_eq!($T::from_str_radix("-9", 2).ok(), None::<$T>);
+                assert_eq!($T::from_str_radix("10_0", 10).ok(), None::<$T>);
+                assert_eq!(u32::from_str_radix("-9", 10).ok(), None::<$T>);
             }
 
             #[test]