patch 8.1.1247: urxvt mouse codes are not tested

Problem:    Urxvt mouse codes are not tested.
Solution:   Also set 'ttymouse' to "urxvt" in the termcodes test.
diff --git a/src/version.c b/src/version.c
index 0e7f3f5..f3e646c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1247,
+/**/
     1246,
 /**/
     1245,