Chore: Add missing void to doc-blocks return types.

[justlevine]

Trac ticket: https://core.trac.wordpress.org/ticket/52217

This PR adds missing void return types to (parent) methods that can explicitly return void as one of their conditional paths.

While these issues were surfaced via PHPStan in #7619 (trac: https://core.trac.wordpress.org/ticket/61175 ), they can be addressed independently of that ticket.

Addressed methods:

• WP_Privacy_Requests_Table::column_status()
• WP_Recovery_Mode::handle_error()
• WP_Widget::form() - unlike the others, it's the child classes that return void when the method is correctly implemented.

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