patch 8.2.2520: missing tests for 'listchars'

Problem:    Missing tests for 'listchars'.
Solution:   Add a few more checks. (Yegappan Lakshmanan, closes #7854)
diff --git a/src/version.c b/src/version.c
index 02abac9..c1d89c0 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2520,
+/**/
     2519,
 /**/
     2518,