test: update cases to silence 'var is never mutated' errors

test/cases/binary_operands.10.zig

@@ -2,6 +2,7 @@ pub fn main() void {
     var i: u32 = 5;
     i *= 7;
     var result: u32 = foo(i, 10);
+    _ = &result;
     if (result != 350) unreachable;
     return;
 }