slow_tests: use strict pointer casting in asm_test.amd64.v (#24461)

Author: tankf33der

vlib/v/slow_tests/assembly/asm_test.amd64.v

@@ -123,7 +123,7 @@ mut:
 fn (m &Manu) str() string {
 	return unsafe {
 		string{
-			str:    m
+			str:    &u8(m)
 			len:    12
 			is_lit: 1
 		}