The issue was caused by `draper` gem upgrade (which was a result of
upgrading Ruby to v3). The issue was here:
https://github.com/drapergem/draper/blob/v4.0.2/lib/draper/automatic_delegation.rb#L10-L26

In decorators we delegate all methods to the decorated object. But this version of the library
only does that when there is no private method with the same name on the decorator.
In this case, as `admin_user`  was a private method on AccountDecorator, draper tried to call
`admin_user `on superclass, but it was not there, so it was failing with:
```
ActionView::Template::Error (super: no superclass method `admin_user' for #<AccountDecorator:0x00007f8784266d18
  @object=#<Account id: 11, org_name: "Testing" ...> Did you mean? admin_user_email):
```

Removing it from `private_methods` fixed the issue.

This test caused multiple tests fail with:
```
ThreadError: deadlock; lock already owned by another fiber belonging to the same thread
```

This is fixed in Rails 7.0.6 and higher: rails/rails#46553

```
DEPRECATION WARNING: Passing a path to `fixture_file_upload` relative to `fixture_path` is deprecated.
In Rails 7.0, the path needs to be relative to `file_fixture_path`.

Please modify the call from
`fixture_file_upload("wide.jpg")` to `fixture_file_upload("../../../test/fixtures/wide.jpg")`.
 (called from block (4 levels) in <main> at /home/dmayorov/Projects/3scale/porta/spec/acceptance/api/cms_file_spec.rb:24)
```

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