patch 8.2.3400: ":z!" is not supported

Problem:    ":z!" is not supported.
Solution:   Make ":z!" work and add tests. (Dominique Pellé, closes #8836)
            Use display height instead of current window height.
diff --git a/src/version.c b/src/version.c
index a9219db..7482d3f 100644
--- a/src/version.c
+++ b/src/version.c
@@ -756,6 +756,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    3400,
+/**/
     3399,
 /**/
     3398,