patch 8.2.3131: MS-Windows: ipv6 channel test is very flaky in the GUI

Problem:    MS-Windows: ipv6 channel test is very flaky in the GUI.
Solution:   Skip the test.
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index 37dfd25..f88cba0 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -252,6 +252,12 @@
 
 func Test_communicate_ipv6()
   CheckIPv6
+
+  " FIXME: this test is very flaky on MS-Windows with the GUI
+  if has('gui_running') && has('win32')
+    throw 'Skipped: test is very flaky with MS-Windows in GUI'
+  endif
+
   call Test_communicate()
 endfunc