Fix typing import circular dependency

Author: Fizzadar

synapse/util/caches/descriptors.py

@@ -17,6 +17,7 @@
 import inspect
 import logging
 from typing import (
+    TYPE_CHECKING,
     Any,
     Awaitable,
     Callable,
@@ -40,13 +41,15 @@
 from twisted.python.failure import Failure
 
 from synapse.logging.context import make_deferred_yieldable, preserve_fn
-from synapse.replication.tcp.external_sharded_cache import ExternalShardedCache
 from synapse.util import unwrapFirstError
 from synapse.util.async_helpers import delay_cancellation
 from synapse.util.caches.deferred_cache import DeferredCache
 from synapse.util.caches.lrucache import LruCache
 from synapse.util.caches.redis_caches import redisCachedList
 
+if TYPE_CHECKING:
+    from synapse.replication.tcp.external_sharded_cache import ExternalShardedCache
+
 logger = logging.getLogger(__name__)
 
 CacheKey = Union[Tuple, Any]