patch 8.2.2920: still a way to shadow a builtin function

Problem:    Still a way to shadow a builtin function. (Yasuhiro Matsumoto)
Solution:   Check the key when using extend(). (issue #8302)
diff --git a/src/version.c b/src/version.c
index a9a7b29..1c01adb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2920,
+/**/
     2919,
 /**/
     2918,