Respect namespace for phabricator importer

What does this MR do and why?

Related to Importers - Default to the current group when i... (#359130 - closed)

This MR correctly reuses namespace_id through import process of phabricator tasks importer. This allows us to correctly select current group as default for import

Screenshots or screen recordings

Projects___Dashboard___GitLab__3_

How to set up and validate locally

1. Open /import/phabricator/new. Observe that first group as selected default
2. Visit any group (except the one you saw on previous step)
3. New project -> Import -> Phabricator tasks
4. Observe that group selected as default import

MR acceptance checklist

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