`entry too large` when update subtask meta of DXF when run using global sort

[D3Hunter]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

when import using global sort, we need to store all the names of generated kv and stat files, the subtask meta might be very large and exceed the default max entry size and report error [kv:8025]entry too large, the max entry size is 6291456, the size of data is 9894491"

in #49237, it add tidb_txn_entry_size_limit to adjust it dynamically, but it only affects for new session, for internal session, as they are always reused, so will not take effects unless handled explicitly, in that PR it only handles add-index, for DXF it won't work.

2. What did you expect to see? (Required)

work

3. What did you see instead (Required)

not

4. What is your TiDB version? (Required)

master