patch 8.2.4043: using int for second argument of ga_init2()

Problem:    Using int for second argument of ga_init2().
Solution:   Remove unnessary type cast (int) when using sizeof().
diff --git a/src/undo.c b/src/undo.c
index ec972f0..4d186d4 100644
--- a/src/undo.c
+++ b/src/undo.c
@@ -3081,7 +3081,7 @@
      */
     mark = ++lastmark;
     nomark = ++lastmark;
-    ga_init2(&ga, (int)sizeof(char *), 20);
+    ga_init2(&ga, sizeof(char *), 20);
 
     uhp = curbuf->b_u_oldhead;
     while (uhp != NULL)