bug: settings changes by set_var hint is not visible when build pipeline in cluster mode

[youngsofun]

Summary

cc @zhang2014 @TCeason

found when debugging my PR, not explicit as an example. I will try to provide an example later.

[TCeason]

Maybe can use this way replace set_var:

set setting=xx;
copy into ...;
unset session setting;

[BohuTANG]

Maybe can use this way replace set_var:

set setting=xx;
copy into ...;
unset session setting;

This is not make sense, the copy is from like python drivers.

[zhang2014]

reproduce: https://github.com/datafuselabs/databend/pull/15596/files#diff-e422a3f3888d72afcada625833a5c984f9665a8ce3d4f32b635e3315e849b717R22