AO3-6811 Fix tag nomination parented bug

[pmonfort]

Pull Request Checklist

• Have you read "How to write the perfect pull request"?
• Have you read the contributing guidelines?
• Have you added tests for any changed functionality?
• Have you added the Jira issue number as the first thing in your pull request title (e.g. AO3-1234 Fix thing)
• Do you have fewer than 5 pull requests already open? If not, please wait until they are reviewed and merged before creating new pull requests.

Issue

https://otwarchive.atlassian.net/browse/AO3-6811

Purpose

When a canonical tag is saved, Tag#update_tag_nominations sets parented: true on matching TagNomination records.
However, it only checked for Fandom-type parents and only matched nominations with a blank parent_tagname (empty string).
This caused nominations to be incorrectly marked as parented: false when:

• The tag's parent was a non-Fandom type (e.g., a Media parent on a Fandom tag).
• The nomination had a nil parent_tagname instead of an empty string.

This PR fixes both issues by:

1. Checking all parent types instead of only Fandoms.
2. Including both "" and nil in the parent_names list so nominations with either blank value are matched.

Testing Instructions

1. Create a canonical fandom tag with a Media parent (but no Fandom parent).
2. Create a tag nomination for that fandom in a tag set.
3. Save the fandom tag.
4. Verify the nomination's parented field is true.

Credit

Pablo Monfort (he/him)

[sarken]

Assigning myself as reviewer since I saw some things I want to poke at, but I am beat so that's not gonna happen tonight

[sarken]

Thanks for working on this! I've updated the Jira issue with new testing steps and just have one question about this code.

[sarken]

I'm not sure this is necessary. A nomination's parent_tagname should always be the name of a fandom unless the nominated tag itself is a fandom. For fandom nominations, it seems like the parent_tagname is always nil, never the name of a media tag. I took a look at staging to confirm:

3.4.6 :001 > noms = FandomNomination.where("parent_tagname IS NOT NULL") ; nil
 => nil 
3.4.6 :002 > noms.size
 => 0 
3.4.6 :003 > noms = FandomNomination.where(parent_tagname: "") ; nil
 => nil 
3.4.6 :004 > noms.size
 => 0 
3.4.6 :005 > noms = FandomNomination.where(parent_tagname: nil) ; nil
 => nil 
3.4.6 :006 > noms.size
 => 21488 
3.4.6 :007 > FandomNomination.all.count
 => 21488

Can you think of a scenario in which we'd expect to find a tag nomination with a non-fandom, non-blank, and non-nil parent_tagname?