patch 8.2.2424: some tests are known to cause an error with ASAN

Problem:    Some tests are known to cause an error with ASAN.
Solution:   Add CheckNotAsan.
diff --git a/src/testdir/test_ex_mode.vim b/src/testdir/test_ex_mode.vim
index a07649e..ffde11e 100644
--- a/src/testdir/test_ex_mode.vim
+++ b/src/testdir/test_ex_mode.vim
@@ -207,6 +207,9 @@
 endfunc
 
 func Test_ex_mode_count_overflow()
+  " The multiplication causes an integer overflow
+  CheckNotAsan
+
   " this used to cause a crash
   let lines =<< trim END
     call feedkeys("\<Esc>Q\<CR>")