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Categories aren't seeded

I followed the instructions [here](https://collab.codidact.org/posts/280451), but even after running `rails db:seed`, there aren't any categories.

Console:

```
moshi@Alpha:~/qpixel$ rails db:create
Running via Spring preloader in process 11391
Created database 'qpixel_dev'
Created database 'qpixel_test'
moshi@Alpha:~/qpixel$ rails db:schema:load
moshi@Alpha:~/qpixel$ rails r db/scripts/create_tags_path_view.rb
Running via Spring preloader in process 11401
moshi@Alpha:~/qpixel$ rails db:migrate
Running via Spring preloader in process 11406
moshi@Alpha:~/qpixel$ rails c
Running via Spring preloader in process 11412
Loading development environment (Rails 7.0.4)
irb(main):001:0> Community.create(name: 'Dev Community', host: 'localhost:3000')
  TRANSACTION (0.6ms)  BEGIN
  Community Exists? (0.9ms)  SELECT 1 AS one FROM `communities` WHERE `communities`.`host` = 'localhost:3000' LIMIT 1
  Community Create (0.5ms)  INSERT INTO `communities` (`name`, `host`, `created_at`, `updated_at`, `is_fake`, `hidden`) VALUES ('Dev Community', 'localhost:3000', '2022-09-19 00:34:06', '2022-09-19 00:34:06', FALSE, FALSE)
  TRANSACTION (16.7ms)  COMMIT
=>
#<Community:0x0000564c6852e710
 id: 1,
 name: "Dev Community",
 host: "localhost:3000",
 created_at: Mon, 19 Sep 2022 00:34:06.000000000 UTC +00:00,
 updated_at: Mon, 19 Sep 2022 00:34:06.000000000 UTC +00:00,
 is_fake: false,
 hidden: false>
irb(main):002:0> Rails.cache.clear
=> nil
moshi@Alpha:~/qpixel$ rails db:seed
Running via Spring preloader in process 11439
PostType: Created 5, skipped 0
CloseReason: Created 5, skipped 0
License: Created 5, skipped 0
TagSet: Created 3, skipped 0
PostHistoryType: Created 12, skipped 0
Ability: Created 7, skipped 0
Category: Created 0, skipped 2
PostFlagType: Created 4, skipped 0
Post: Created 15, skipped 5
ReactionType: Created 3, skipped 0
SiteSetting: Created 67, skipped 0
User: Created 1, skipped 0
WarningTemplate: Created 3, skipped 0
```

http://localhost:3000/categories:

![Image alt text](https://collab.codidact.org/uploads/E5aSnsrYRecWcoLgEUonE8V3)

Checking via console:
```
moshi@Alpha:~/qpixel$ rails c
Running via Spring preloader in process 11500
Loading development environment (Rails 7.0.4)
irb(main):001:0> Category.all.to_a
  Category Load (0.6ms)  SELECT `categories`.* FROM `categories` WHERE `categories`.`community_id` IS NULL
=> []
```

Clearly, the categories haven't been seeded. What did I do wrong, and how do I fix this?