ref(client): Fix type checking with fallback asynctransport

GH-4601

Author: srothh

sentry_sdk/client.py

@@ -959,7 +959,9 @@ async def _flush_and_close(
             await self._close_components_async()
 
         if self.transport is not None:
-            if isinstance(self.transport, AsyncHttpTransport):
+            if isinstance(self.transport, AsyncHttpTransport) and hasattr(
+                self.transport, "loop"
+            ):
 
                 try:
                     flush_task = self.transport.loop.create_task(
@@ -996,7 +998,9 @@ def flush(  # type: ignore[override]
             if timeout is None:
                 timeout = self.options["shutdown_timeout"]
 
-            if isinstance(self.transport, AsyncHttpTransport):
+            if isinstance(self.transport, AsyncHttpTransport) and hasattr(
+                self.transport, "loop"
+            ):
                 try:
                     return self.transport.loop.create_task(
                         self._flush_async(timeout, callback)

sentry_sdk/transport.py

@@ -29,6 +29,8 @@
     HTTP2_ENABLED = False
 
 try:
+    import anyio  # noqa: F401
+
     ASYNC_TRANSPORT_ENABLED = httpcore is not None
 except ImportError:
     ASYNC_TRANSPORT_ENABLED = False