Refactor Elasticsearch Indexed Containers specs to support parent strategy

What does this MR do?

Related to #240929 (closed)

The MR !40274 (merged) implements using parent strategy for associations in factories (see factory_bot docs) by removing FactoryBot.use_parent_strategy = false from factory_bot.rb, but that results in several failures that need to be fixed and merged in advance.

As @engwan kindly fixed all fallings and committed them individually, we just need to cherry-pick them and deliver them as their own MRs.

This specific MR contains the cherry-picked commit a8f95ec9 that fixes failings in

• ee/spec/models/elasticsearch_indexed_namespace_spec.rb
• ee/spec/models/elasticsearch_indexed_project_spec.rb
• ee/spec/models/gitlab_subscription_spec.rb
• ee/spec/support/shared_examples/models/elasticsearch_indexed_container_shared_examples.rb

For more context:

Heinrich Lee Yu @engwan commented:

I managed to fix the failures in !40274 (merged). Anyone want to create MRs from the commits there? 🙂 There are 42 commits and most should pass as their own MRs. I also put the explanation in the commit message. So, picking commits there should count as a review, then you can pass it on to a maintainer. 🙂

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Does this MR meet the acceptance criteria?

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