testsuite: Mark T13167 as fragile in threaded2

As noted in #16536.

libraries/base/tests/all.T

@@ -234,6 +234,6 @@ test('T3474',
 test('T14425', normal, compile_and_run, [''])
 test('T10412', normal, compile_and_run, [''])
 test('T13896', normal, compile_and_run, [''])
-test('T13167', normal, compile_and_run, [''])
+test('T13167', fragile_for(16536, ['threaded2']), compile_and_run, [''])
 test('T15349', [exit_code(1), expect_broken_for(15349, 'ghci')], compile_and_run, [''])
 test('T16111', exit_code(1), compile_and_run, [''])