CMS10: Scheduled publishing two languages of same page causes validation error

Description

Steps to reproduce

1. Install an Alloy sample site.
2. Create a new page in English (EN) and set the scheduled publish ahead in time (use the default tomorrow as 12).
3. Translate the page to Swedish (SV).
4. Choose scheduled publishing for the SV version and pick the same datestamp as in 2. It does not matter if you pick a later time; the same error appears.
5. Click the Schedule button.

Expected: You can schedule the publishing of a SV version page.
Actual: An error appears, and the page is not set to publish in the future.

Note: This is a hotfix of CMS-8941 also fixed in CMS 11.