patch 9.0.0894: virtual text property highlight ignores window background

Problem:    Virtual text property highlight ignores window background.
Solution:   Combine text prop attribute with win_attr into extra_attr.
            (closes #11462)

src/version.c

@@ -695,6 +695,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    894,
 /**/
     893,
 /**/