* ddl: delay before changing column from null to not null
Signed-off-by: Yilin Chen <sticnarf@gmail.com>
Co-authored-by: Ti Chi Robot <71242396+ti-chi-bot@users.noreply.github.com>
Co-authored-by: Arenatlx <314806019@qq.com>

Signed-off-by: AilinKid <314806019@qq.com>

Signed-off-by: crazycs520 <crazycs520@gmail.com>

* ddl: handle store closed in doDDLJob

* fix typo

* fix test

* fix test

* address comment

* address comments

* fix test

* address comment

* address comment

* fix data race

* fix data race

* don't repeat code

* address comment

* adress comment

* avoid failpoint change between two injection

* add comments

* change behaviour, fix test

* fix build option

* remove used variable

* Revert "remove used variable"

This reverts commit df93c431163515a496015f20f323ea91480f0020.

* modify comment

* try fix deadlock

* try fix deadlock

* try fix test
Co-authored-by: Arenatlx <ailinsilence4@gmail.com>
Co-authored-by: Lynn <zimu_xia@126.com>