patch 8.2.1304: debug backtrace isn't tested much

Problem:    Debug backtrace isn't tested much.
Solution:   Add more specific tests. (Ben Jackson, closes #6540)
diff --git a/src/version.c b/src/version.c
index 73ab8c3..c41d932 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1304,
+/**/
     1303,
 /**/
     1302,