patch 8.1.2400: test39 is old style

Problem:    Test39 is old style.
Solution:   Convert the test cases into new style. (Yegappan Lakshmanan,
            closes #5324)
diff --git a/src/version.c b/src/version.c
index 4ca28a5..8d4f945 100644
--- a/src/version.c
+++ b/src/version.c
@@ -743,6 +743,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2400,
+/**/
     2399,
 /**/
     2398,