the standby node is unable to view the citus_tables view when backing up the database.

[wkz2797848480]

How to reproduce
Database version: PostgreSQL 16.6 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5
Citus version: Citus 12.1.4 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.5

Problem Description:

In a Patroni-based high-availability environment for Citus cluster backup, the standby node is unable to view the citus_tables view when backing up the database.

Executing commands on Coordinator/Worker nodes results in an error description：
postgres=# select * from citus_shard_sizes() css(shard_id, size);
ERROR: writing to worker nodes is not currently allowed
DETAIL: the database is read-only
postgres=# select * from citus_tables;
ERROR: writing to worker nodes is not currently allowed
DETAIL: the database is read-only