This breaking change was originally a deprecation fix for overriding a computed property `none`.
There are 4 uses of `rootNone` in core and "all-the-plugins":
1. in discourse-chat-integration, admin-plugins-chat-edit-rule.hbs - changed behavior, that I'd consider a fix - `rootNoneLabel` is now used regardless of `siteSettings.allow_uncategorized_topics` value, which I believe was an originally intended behavior (i.e. it most likely hasn't been tested with disabled uncategorized topics)
2. in discourse-slack-official, plugins-slack.hbs - the same as 1.
3. in core, edit-category-general.hbs (in this PR) - no change in behavior
4. in discourse-googlebooks, edit-category-general.hbs - no change in behavior (since `allowUncategorized="true"` is also passed as an argument)
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