Fix broken test for "remove_last_char_works_with_normal_string"

I accidentally "fixed" the missing char in the previous commit.

src/utils/text_manipulation.rs

@@ -26,7 +26,7 @@ mod test {
     fn remove_last_char_works_with_normal_string() {
         let string = "this is a string";
 
-        assert_eq!(remove_last_grapheme(string), "this is a string");
+        assert_eq!(remove_last_grapheme(string), "this is a strin");
     }
 
     #[test]