Use the set date instead of getDate()

[andizer]

Summary

This PR can be summarized in the following changelog entry:

• [@yoast/schema-blocks] Fixes a bug where todays date will be shown always no matter which date is chosen.

Relevant technical choices:

Test instructions

This PR can be tested by following these steps:

• Add a job posting
• Select a date for the closes on block
• See that the value is the date that has been selected.

Impact check

• This PR affects the following parts of the plugin, which may require extra testing:
  *

UI changes

• This PR changes the UI in the plugin. I have added the 'UI change' label to this PR.

Quality assurance

• I have tested this code to the best of my abilities
• I have added unittests to verify the code works as intended

Fixes #

[hansjovis]

Acceptance: ✅