patch 9.0.0851: terminal mouse test is still flaky

Problem:    Terminal mouse test is still flaky.
Solution:   Also use WaitForAssert().
diff --git a/src/testdir/test_terminal3.vim b/src/testdir/test_terminal3.vim
index 59fba96..f871187 100644
--- a/src/testdir/test_terminal3.vim
+++ b/src/testdir/test_terminal3.vim
@@ -716,7 +716,7 @@
   call TermWait(buf, 50)
   call term_sendkeys(buf, ":call writefile([@\"], 'Xbuf')\<CR>")
   call WaitFor(XbufExists)
-  call assert_equal('yellow', readfile('Xbuf')[0])
+  call WaitForAssert({-> assert_equal('yellow', readfile('Xbuf')[0])})
   call delete('Xbuf')
 
   " Test for selecting text using double click
diff --git a/src/version.c b/src/version.c
index 3433ebc..cb95d2c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    851,
+/**/
     850,
 /**/
     849,