patch 8.0.0956: scrolling in a terminal window has flicker

Problem:    Scrolling in a terminal hwindow as flicker when the Normal
            background differs from the terminal window background.
Solution:   Set the attribute to clear with.
diff --git a/src/version.c b/src/version.c
index 9859b4a..f02af88 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    956,
+/**/
     955,
 /**/
     954,