Fix incorrect test

The test was added 11 days ago[^1] and is not part of 6.c-errata.

Negative exponents underflow, not overflow.

[1] 714abc9

Author: zoffixznet

S03-operators/overflow.t

@@ -266,7 +266,7 @@ sub tryeq_sloppy ($lhs, $rhs, $todo1 = '') {
 throws-like '2**10000000000', X::Numeric::Overflow,
     'attempting to raise to a huge power throws';
 
-throws-like '2**-10000000000', X::Numeric::Overflow,
+throws-like '2**-10000000000', X::Numeric::Underflow,
     'attempting to raise to a huge negative power throws';
 
 # vim: ft=perl6