patch 8.2.0402: setting local instead of global flag

Problem:    Setting local instead of global flag.
Solution:   Prepend "g:" to "test_is_flaky".
diff --git a/src/testdir/term_util.vim b/src/testdir/term_util.vim
index c9e0ac5..dd1f71d 100644
--- a/src/testdir/term_util.vim
+++ b/src/testdir/term_util.vim
@@ -94,7 +94,7 @@
   endtry
 
   " Starting a terminal to run Vim is always considered flaky.
-  let test_is_flaky = 1
+  let g:test_is_flaky = 1
 
   return buf
 endfunc
@@ -102,7 +102,7 @@
 " Stop a Vim running in terminal buffer "buf".
 func StopVimInTerminal(buf)
   " Using a terminal to run Vim is always considered flaky.
-  let test_is_flaky = 1
+  let g:test_is_flaky = 1
 
   call assert_equal("running", term_getstatus(a:buf))