Restrict permissions of github workflow

Author: lukasbindreiter

.github/workflows/main.yml

@@ -1,5 +1,7 @@
 name: CI
 
+permissions: {}
+
 on:
   push:
     branches: [main]

tilebox-grpc/_tilebox/grpc/channel.py

@@ -43,6 +43,7 @@
     ("grpc.service_config", json.dumps(_SERVICE_CONFIG)),
 ]
 
+
 class ChannelProtocol(Enum):
     HTTPS = 1
     HTTP = 2