Fixed a CaptureQueriesContext usage in queries tests.

tests/queries/tests.py

@@ -1950,7 +1950,7 @@ class ExistsSql(TestCase):
             self.assertFalse(Tag.objects.exists())
         # Ok - so the exist query worked - but did it include too many columns?
         self.assertEqual(len(captured_queries), 1)
-        qstr = captured_queries[0]
+        qstr = captured_queries[0]['sql']
         id, name = connection.ops.quote_name('id'), connection.ops.quote_name('name')
         self.assertNotIn(id, qstr)
         self.assertNotIn(name, qstr)