patch 8.1.1573: textprop test fails if screenhots do not work

Problem:    Textprop test fails if screenhots do not work.
Solution:   Add check for screenhots working.
diff --git a/src/version.c b/src/version.c
index 62ef113..9060ceb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1573,
+/**/
     1572,
 /**/
     1571,