Ignore warnings from third-parties during tests

pytest.ini

@@ -26,3 +26,5 @@ filterwarnings =
     ignore:Module scrapy.utils.reqser is deprecated
     ignore:typing.re is deprecated
     ignore:typing.io is deprecated
+    ignore:::h2
+    ignore:::w3lib

scrapy/core/downloader/__init__.py

@@ -350,6 +350,7 @@ class Downloader:
         self._slot_gc_loop.stop()
         for slot in self.slots.values():
             slot.close()
+        self._record_backout(None)
 
     def _slot_gc(self, age: float = 60) -> None:
         mintime = time() - age