Add a workaround for the clickhouse 24.9+ problem causing an error (#12767)

## Problem
We used ClickHouse v. 24.8, which is outdated, for logical replication
testing. We could miss some problems.
## Summary of changes
The version was updated to 25.6, with a workaround using the environment
variable `PGSSLCERT`.

Co-authored-by: Alexey Masterov <alexey.masterov@databricks.com>

.github/workflows/pg-clients.yml

@@ -72,9 +72,10 @@ jobs:
       options: --init --user root
     services:
       clickhouse:
-        image: clickhouse/clickhouse-server:24.8
+        image: clickhouse/clickhouse-server:25.6
         env:
           CLICKHOUSE_PASSWORD: ${{ needs.generate-ch-tmppw.outputs.tmp_val }}
+          PGSSLCERT: /tmp/postgresql.crt
         ports:
           - 9000:9000
           - 8123:8123