Add missing `group` local assigns definition to HAML partials

📖 What does this MR do?

In !61180 (merged) I refactored some Cascading settings HAML partials. In !61418 (diffs) I documented these HAML partials. I noticed a typo where the group argument is required for these partials to work but it is not defined at the top of the HAML partials and it is not documented. We are, however, passing the group argument to the partials in the one place these are currently used: ee/app/views/groups/settings/_delayed_project_removal.html.haml#L9. Functionally this doesn't change anything as the partials worked before this change (and after 😆). This MR aims to improve discoverability and developer experience when using these partials.

🚦 Does this MR meet the acceptance criteria?

Conformity

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  • Not needed, developer facing change and docs change
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Availability and Testing

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Security

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• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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