Fix a typo: we need do we need to -> we need to

Morning delirium does not help when looking at lots of words

exercises/108_labeled_switch.zig

@@ -47,7 +47,7 @@
 //        but instead the value to be evaluated is now '3';
 //  4. Finally we get to case '3', where we return from the function as a whole.
 //  5. In this example as the input has no clear exhaustive patterns but a essentially
-//      any u8 integer, we need do need to handle any case that is not explicitly handled
+//      any u8 integer, we need to handle any case that is not explicitly handled
 //      by using the `else => {}` branch as a default case.
 //
 // Since step 4 or a break stament do not exist in this switch, the debug statement is