Fix inconsistent returned value of airflow dags next-execution cli command

[boushphong]

closes: #22474

• This commit is to fix the inconsistent returned value of airflow dags next-execution cli command when the dag is paused and catchup is False

In brief:

• When the dag is unpaused, the cli command would get the next-execution run from the DagRun model. However, when the dag is paused, getting the next-execution run from the DagRun model would yield the next dag run time from the last executed dag run, which is incorrect as time passes.
• To avoid this, we can get the next-execution run time from dag_model.next_dag_run (as in: dag.html L143) to make it more consistent with the UI.

Modification:

• Use only the DagModel to get a dag next execution info. This way we could:
  • Handle the catchup=False case and when the Dag is paused.
  • Handle the case of next execution info is None when args.num_executions is specified. Previous code will throw an error as follow: None type has no attribute logical_date ...
  • Modify test case to handle all dag parsing scenarios.

This is my first PR, please let me know if there is anything I could do differently.

[boring-cyborg]

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[uranusjr]

Hmm, I think I prefer the previous range(1, num) way.

[boushphong]

I think the range(1, num) way would require handling and printing None in 2 different places. 1 before the loop and 1 more within the for loop itself. I just think the handling all those cases within the loop would be more elegant. But if you insist ... 😅

[uranusjr]

Personally I feel handling in two places is actually easier than having to check for 0 every time. If you really hate code duplication, you can define a local function to reuse the logic. But checking for the index in the loop almost always makes things unnecessarily complex.

[boushphong]

Right, will do!

[boushphong]

@uranusjr Just updated the PR's description. This PR is ready for review 🙇

[huymq1710]

LGTM

[boring-cyborg]

Awesome work, congrats on your first merged pull request!