[Backport] Fix import grouped products #12853

[insanityinside]

Backport of relevant code from 9c9f2f3 from PR ##12853

[magento-engcom-team]

Hi @insanityinside. Thank you for your contribution
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[magento-engcom-team]

Hi @VladimirZaets, thank you for the review.
ENGCOM-3003 has been created to process this Pull Request

[magento-engcom-team]

Hi @insanityinside. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.