The ArgumentError occurs even though structures is compatible.
Because some query methods keep duplicate values.

For example, the behavior of `joins` method is as following:

```ruby
relation = Post.joins(:author).joins(:author)
relation.joins_values
#=> [:author, :author]
relation.or(Post.joins(:author))
#=> ArgumentError: Relation passed to #or must be structurally compatible. Incompatible values: [:joins]
```

This commit changes to not keep duplicate values.

Fixes #38052