[core] Fix collecting wrong sorted runs when compacting on custom branch

[schnappi17]

Purpose

Linked issue: subtask #2861

When writing to a custom branch, the compaction within writer will picking the wrong sorted runs on the 'main' branch to compact, which will cause the commit conflict, like willing to delete files which never been added.

Tests

API and Format

Documentation

[sunxiaojian]

@schnappi17 If https://github.com/apache/incubator-paimon/pull/3029 Merged, do we no longer need the current processing method ?

[schnappi17]

Fixed in https://github.com/apache/paimon/pull/3029, close this.