Fix ambiguous namespace_id in query

What does this MR do and why?

Fix ambiguous namespace_id in query

When using in_namespaces_with_cte the query can become ambiguous if there are other namespace_id's joined.

Changelog: fixed

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Before	After

How to set up and validate locally

For example, joining the work_item_type didn't work since it also has a namespace_id column.

ctiveRecord::StatementInvalid: PG::AmbiguousColumn: ERROR:  column reference "namespace_id" is ambiguous
LINE 1: ...types"."id" = "issues"."work_item_type_id" WHERE (namespace_...

Before

::WorkItems::WorkItemsFinder.new(User.first, group_id: Group.first.id).execute.with_work_item_type.first # => error

After

::WorkItems::WorkItemsFinder.new(User.first, group_id: Group.first.id).execute.with_work_item_type.first