Copy multilingual doc should not copy reference to translated doc

We found an issue with copying translated documents in 7.9. It looks like the translation id is copied. It is not possible to make a translated document of a copied document.

Reproduction path using archetype 1.09.00 with following overrides:
<hippo.hst.version>2.28.03</hippo.hst.version>
<hippo.repository.version>2.26.03</hippo.repository.version>
<hippo.cms.version>2.26.03</hippo.cms.version>
<hippo.addon-channel-manager.version>2.26.01</hippo.addon-channel-manager.version>

Reproduction:

• Login cms as admin
• Create new root language (Dutch)
• Link the news folder to nieuws (Dutch)
• Create a Dutch translation of the Toyota news document
• Copy the Toyota news document
• Click on the translation of the copy

Expected:
Dialog opens for creating a new translation

Result:
The translated document in Dutch opens. In the console the translation id is copied. If the translation id field is made empty, the dialog for creating new translation opens again.

Looks very similar to https://issues.onehippo.com/browse/CMS7-5343