fix: running nodes should not include replica nodes

[JimMoen]

Fixes EMQX-9413

Summary

🤖 Generated by Copilot at 53712e6

Fixed a cluster configuration issue and updated the emqx_conf application and change logs. The fix uses mria_mnesia:running_nodes to get cluster nodes and prevents copying cluster-override.conf from a replica node.

PR Checklist

Please convert it to a draft if any of the following conditions are not met. Reviewers may skip over until all the items are checked:

• Added tests for the changes
• Changed lines covered in coverage report
• Change log has been added to changes/{ce,ee}/(feat|perf|fix)-<PR-id>.en.md files
• For internal contributor: there is a jira ticket to track this change
• If there should be document changes, a PR to emqx-docs.git is sent, or a jira ticket is created to follow up
• Schema changes are backward compatible

Checklist for CI (.github/workflows) changes

• If changed package build workflow, pass this action (manual trigger)
• Change log has been added to changes/ dir for user-facing artifacts update

[JimMoen]

It's a revert for part of changes in #7731