Fix migration 0080_2_0_2 - Replace null values before setting column not null

[tm-drtina]

Partially reverts change from #20962 where update to NULL values was dropped.
Default only applies to INSERTs and UPDATEs or newly added columns (at least in postgres), so if the column contained NULLs before, the migration fails.

closes: #24566

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[boring-cyborg]

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[github-actions]

The PR most likely needs to run full matrix of tests because it modifies parts of the core of Airflow. However, committers might decide to merge it quickly and take the risk. If they don't merge it quickly - please rebase it to the latest main at your convenience, or amend the last commit of the PR, and push it with --force-with-lease.

[tm-drtina]

Maybe I misunderstood the message, but I though I had to rebase the PR. Anyway the pull of python image failed due to unauthenticated access.

error pulling image configuration: unauthorized: unauthenticated: User cannot be authenticated with the token provided.
There was an error pulling the image 3.7. Failing.
There was an error when pulling CI image: Image Python 3.7

[uranusjr]

It’s not you, GitHub was having issues.

[potiuk]

I re-run to rebuild because we updated big set of dependency changes yesterday (FAB 4.1.1) and second build failed due to constraints there.

[boring-cyborg]

Awesome work, congrats on your first merged pull request!