Update part9c.md

Typo fix:
exeption -> exception

Author: romanstetsyk

src/content/9/en/part9c.md

@@ -1368,7 +1368,7 @@ const toNewDiaryEntry = (object: unknown): NewDiaryEntry => {
 };
 ```
 
-If the guard does not evaluate to true, an exeption is thrown.
+If the guard does not evaluate to true, an exception is thrown.
 
 The use of operator *in* actually now guarantees that the fields indeed exist in the object. Because of that, the existence check in parsers in no more needed: