grpc: fix line formatting

Author: Nazarevsky

contrib/pyln-grpc-proto/pyln/grpc/node_pb2_grpc.py

@@ -18,7 +18,7 @@
 if _version_not_supported:
     raise RuntimeError(
         f'The grpc package installed is at version {GRPC_VERSION},'
-        + ' but the generated code in node_pb2_grpc.py depends on'
+        + f' but the generated code in node_pb2_grpc.py depends on'
         + f' grpcio>={GRPC_GENERATED_VERSION}.'
         + f' Please upgrade your grpc module to grpcio>={GRPC_GENERATED_VERSION}'
         + f' or downgrade your generated code using grpcio-tools<={GRPC_VERSION}.'