Fix 'start_in' not updated while 'when' is selected as 'delayed'

What does this MR do and why?

When user select When to delayed in job assistant rules section, the start_in should be updated in parent component, otherwise splitting an unintialized could throw error when add the job to editor.

Screenshots or screen recordings

Before	After
QQ20230703-212639-HD	QQ20230703-213511-HD

How to set up and validate locally

1. Enable the feature flag

   Feature.enable(:ci_job_assistant_drawer)

2. Visit any CI editor pages such as http://127.0.0.1:3000/root/demo/-/ci/editor?branch_name=master

3. Click the job assistant button.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

/cc @daveliu @JeremyWuuuuu @fenyuluoshang