patch 8.1.1176: test for dragging a tab is flaky

Problem:    Test for dragging a tab is flaky.
Solution:   Add a brief sleep.

src/testdir/test_termcodes.vim

@@ -325,6 +325,8 @@ func Test_xterm_mouse_drag_to_move_tab()
         \              'Tab page 2',
         \              '    Xtab1'], a)
 
+    " brief sleep to avoid causing a double-click
+    sleep 20m
     %bwipe!
   endfor
 

src/version.c

@@ -771,6 +771,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1176,
 /**/
     1175,
 /**/