patch 8.2.4603: sourcing buffer lines is too complicated

Problem:    Sourcing buffer lines is too complicated.
Solution:   Simplify the code. Make it possible to source Vim9 script lines.
            (Yegappan Lakshmanan, closes #9974)
diff --git a/src/version.c b/src/version.c
index e262953..3874b93 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4603,
+/**/
     4602,
 /**/
     4601,