Correctly restore warning capture after logging tests.

This is a fix to the wrong behavior that 15c3906eeb introduced.

tests/logging_tests/tests.py

@@ -96,7 +96,9 @@ class WarningLoggerTests(TestCase):
         # If tests are invoke with "-Wall" (or any -W flag actually) then
         # warning logging gets disabled (see django/conf/__init__.py). However,
         # these tests expect warnings to be logged, so manually force warnings
-        # to the logs.
+        # to the logs. Use getattr() here because the logging capture state is
+        # undocumented and (I assume) brittle.
+        self._old_capture_state = bool(getattr(logging, '_warnings_showwarning', False))
         logging.captureWarnings(True)
 
         # this convoluted setup is to avoid printing this deprecation to
@@ -115,7 +117,7 @@ class WarningLoggerTests(TestCase):
             self.logger.handlers[i].stream = self.old_streams[i]
 
         # Reset warnings state.
-        logging.captureWarnings(False)
+        logging.captureWarnings(self._old_capture_state)
 
     @override_settings(DEBUG=True)
     def test_warnings_capture(self):