patch 9.0.1625: "super" is not considered a reserved name

Problem:    "super" is not considered a reserved name.
Solution:   Add "super" to the list of reserved names. (closes #12515)
diff --git a/src/vim9script.c b/src/vim9script.c
index b1849db..a64ce72 100644
--- a/src/vim9script.c
+++ b/src/vim9script.c
@@ -1122,6 +1122,7 @@
     "null_string",
     "null_channel",
     "null_job",
+    "super",
     "this",
     NULL
 };