patch 9.0.1009: test for catch after interrupt is flaky on MS-Windows

Problem:    Test for catch after interrupt is flaky on MS-Windows.
Solution:   Mark the test as flaky.

src/testdir/test_vimscript.vim

@@ -6017,6 +6017,9 @@ endfunc
 
 " interrupt right before a catch is invoked inside a function.
 func Test_ignore_catch_after_intr_2()
+  " for unknown reasons this test sometimes fails on MS-Windows.
+  let g:test_is_flaky = 1
+
   XpathINIT
   func F()
     try