patch 8.1.1020: compiler warning for Python3 interface

Problem:    Compiler warning for Python3 interface.
Solution:   Add type cast. (Ozaki Kiichi, closes #4128, closes #4103)
diff --git a/src/version.c b/src/version.c
index a32770e..c336046 100644
--- a/src/version.c
+++ b/src/version.c
@@ -780,6 +780,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1020,
+/**/
     1019,
 /**/
     1018,