patch 8.1.0966: one terminal test is flaky

Problem:    One terminal test is flaky.
Solution:   Add to list of flaky tests.
diff --git a/src/testdir/runtest.vim b/src/testdir/runtest.vim
index 383e627..9108b8e 100644
--- a/src/testdir/runtest.vim
+++ b/src/testdir/runtest.vim
@@ -307,6 +307,7 @@
       \ 'Test_terminal_ansicolors_func()',
       \ 'Test_terminal_ansicolors_global()',
       \ 'Test_terminal_composing_unicode()',
+      \ 'Test_terminal_does_not_truncate_last_newlines()',
       \ 'Test_terminal_env()',
       \ 'Test_terminal_hide_buffer()',
       \ 'Test_terminal_make_change()',