Update upgrading guide

Author: Pijukatel

docs/04_upgrading/upgrading_to_v3.md

@@ -50,7 +50,7 @@ async def main():
 - `Configuration.default_dataset_id` changed from `'default'` to `None`.
 - `Configuration.default_request_queue_id` changed from `'default'` to `None`.
 
-As a consequence of this change, using default storage without specifying its `id` in `Configuration` will use unnamed storage.
+Previously using the default storage without specifying its `id` in `Configuration` would lead to using specific storage with id `'default'`. Now it will use newly created unnamed storage with `'id'` assigned by the Apify platform, consecutive calls to get the default storage will return the same storage.
 
 ## Storages
 

tests/integration/test_apify_storages.py

@@ -45,7 +45,13 @@ async def test_unnamed_default_without_config(
     service_locator.set_configuration(Configuration(token=apify_token))
     service_locator.set_storage_client(ApifyStorageClient())
 
+    # Open storage and make sure it has no name and it has id
     storage = await storage_type.open()
     assert storage.name is None
     assert storage.id
+
+    # Make sure the same instance is returned when opened again without name or alias
+    storage_again = await storage_type.open()
+    assert storage is storage_again
+
     await storage.drop()