Rectify moth and day placeholders in DIT633/README.md

This is to avoid any confusion with the date format. The date format
should be consistent throughout the repository.

exams/DIT633/README.md

@@ -6,10 +6,10 @@ Here’s what we have so far:
 * 2021-03-16 Home exam questions with teacher answers
 * 2021-06-02 Home exam questions with no student answers so far
 * 2021-08-27 Home exam questions with no student answers so far
-* 2022-YY-DD Several exam questions with no student answers so far
+* 2022-MM-DD Several exam questions with no student answers so far
 * 2023-03-16 Exam questions with student answers
 > Note: there's some mistakes in the solutions, hence, we encourage not to rely
 > solely on these answers. Still, the exam is useful for practice.
-* 2023-YY-DD Several exam questions with no student answers so far
+* 2023-MM-DD Several exam questions with no student answers so far
 > We could not find when exactly the exams were held, so they are placed in the
 > '2023' folder.