Fix excerpt generation to include list-item block content in excerpts

[geekofshire]

This PR resolves an issue where content within list-item blocks was excluded from post excerpts. The function excerpt_remove_blocks() now allows core/list-item as part of $allowed_inner_blocks, ensuring that list content is correctly included in generated excerpts.

Trac ticket: https://core.trac.wordpress.org/ticket/62417

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