Normalized exercise output, answers (#41)

1. All exercises should print a trailing \n
2. The build script should always show you _exactly_ what it's looking
   for when you get it wrong. Therefore, .output should be set to the
   exact expected output.

exercises/023_errors3.zig

@@ -14,7 +14,7 @@ pub fn main() void {
     var a: u32 = addTwenty(44) catch 22;
     var b: u32 = addTwenty(4) ??? 22;
 
-    std.debug.print("a={}, b={}", .{ a, b });
+    std.debug.print("a={}, b={}\n", .{ a, b });
 }
 
 // Please provide the return type from this function.