docs(storage): clarify docstring for 'Blob.download_as_string' (#9332)

Specify that the returned value is bytes in the summary.

Closes #9290.

storage/docs/snippets.py

@@ -39,7 +39,7 @@ def storage_get_started(client, to_delete):
     bucket = client.get_bucket("bucket-id-here")
     # Then do other things...
     blob = bucket.get_blob("/remote/path/to/file.txt")
-    assert blob.download_as_string() == "My old contents!"
+    assert blob.download_as_string() == b"My old contents!"
     blob.upload_from_string("New contents!")
     blob2 = bucket.blob("/remote/path/storage.txt")
     blob2.upload_from_filename(filename="/local/path.txt")

storage/google/cloud/storage/blob.py

@@ -712,7 +712,7 @@ def download_to_filename(self, filename, client=None, start=None, end=None):
             os.utime(file_obj.name, (mtime, mtime))
 
     def download_as_string(self, client=None, start=None, end=None):
-        """Download the contents of this blob as a string.
+        """Download the contents of this blob as a bytes object.
 
         If :attr:`user_project` is set on the bucket, bills the API request
         to that project.