…`ClassInstanceVariable`

```
lib/tanshuku.rb:18:5: W: Lint/RedundantCopDisableDirective: Unnecessary disabling of ThreadSafety/InstanceVariableInClassMethod (did you mean ThreadSafety/ClassInstanceVariable?).
    # rubocop:disable ThreadSafety/InstanceVariableInClassMethod
    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
lib/tanshuku.rb:19:5: C: ThreadSafety/ClassInstanceVariable: Avoid class instance variables.
    @config ||= Configuration.new
    ^^^^^^^
```

```
lib/tasks/check_all.rb:24:32: C: ThreadSafety/NewThread: Avoid starting new threads.
    TASKNAMES.map { |taskname| Thread.new(taskname, &executor) }.each(&:join)
                               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```

```
tanshuku.gemspec:30:5: C: ThreadSafety/DirChdir: Avoid using Dir.chdir due to its process-wide effect.
    Dir.chdir(__dir__) do
    ^^^^^^^^^^^^^^^^^^
```

```
spec/models/tanshuku/url_spec.rb:195:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0]).to be_a ArgumentError
                                  ^^^
spec/models/tanshuku/url_spec.rb:210:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0]).to be_a ActiveRecord::RecordInvalid
                                  ^^^
spec/models/tanshuku/url_spec.rb:211:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0].record.errors).to be_of_kind :url, :blank
                                  ^^^
spec/models/tanshuku/url_spec.rb:226:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0]).to be_a ActiveRecord::RecordInvalid
                                  ^^^
spec/models/tanshuku/url_spec.rb:227:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0].record.errors).to be_of_kind :url, :invalid
                                  ^^^
spec/models/tanshuku/url_spec.rb:463:37: C: [Correctable] Style/ArrayFirstLast: Use first.
          expect(reported_exceptions[0]).to be_a ActiveRecord::RecordNotFound
                                    ^^^
spec/models/tanshuku/url_spec.rb:483:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0]).to be_a ArgumentError
                                  ^^^
spec/models/tanshuku/url_spec.rb:484:35: C: [Correctable] Style/ArrayFirstLast: Use first.
        expect(reported_exceptions[0].message).to match(/Missing host to link to!/)
                                  ^^^
```

cf. #331 (comment)

> The CI is failing because [the current version of Rails doesn’t support `sqlite3` v2](https://github.com/rails/rails/blob/v7.1.3.2/activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb#L14). We need to wait for the next release of Rails.

v2: support Ruby 3.1 and Rails 7.0 and 7.1