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

test/cases/while_loops.2.zig

@@ -2,6 +2,7 @@ pub fn main() u8 {
     var i: u8 = 0;
     while (i < @as(u8, 10)) {
         var x: u8 = 1;
+        _ = &x;
         i += x;
         if (i == @as(u8, 5)) break;
     }