Restore signed isqrt implementation to original, but using panic function

Author: ChaiTRex

library/core/src/num/int_macros.rs

@@ -2800,10 +2800,9 @@ macro_rules! int_impl {
         #[inline]
         #[track_caller]
         pub const fn isqrt(self) -> Self {
-            if let Some(sqrt) = self.checked_isqrt() {
-                sqrt
-            } else {
-                crate::num::int_sqrt::panic_for_negative_argument()
+            match self.checked_isqrt() {
+                Some(sqrt) => sqrt,
+                None => crate::num::int_sqrt::panic_for_negative_argument(),
             }
         }