This fixes a regression introduced by 6cc03675.

ActiveRecord, if used without Rails, always checks the "default_env" environment. This would be OK, except that Sinatra also supports environments,
and it runs with {RACK|RAILS}_ENV=production. This patch adds a fallback to RAILS_ENV and RACK_ENV (and ultimately default_env) if Rails.env doesn't exist.

fix small typo in routing test

Fix url generation error message

Provide more reasoning to not accept cosmetic changes [ci skip]

Activejob cleanups

Remove duplicate 'select' database statement

AJ doc fixes [ci skip]

[ci skip]

- Fix mentioned shortcut, to what the shortcut actually is, and that it accepts blocks for `assert_no_enqueued_jobs` and `assert_no_performed_jobs` test helpers.
- args => arguments when used in actual docs.

[ci skip]

The `select` method has the same definition in almost all database
adapters, so it can be moved from the database-specific adapters
(PostgreSQl, MySQL, SQLite) to the abstract `database_statement`:

```ruby
def select(sql, name = nil, binds = [])
  exec_query(sql, name, binds)
end
```

---

More details about this commit: the only two DB-specific adapters
that have a different definition of `select` are MySQLAdapter and
MySQL2Adapter.

In MySQLAdapter, `select` invokes `exec_query(sql, name, binds)`, so
calling `super` achieves the same goal with less repetition.

In MySQL2Adapter, `select` invokes `exec_query(sql, name)`, that is,
it does not pass the `binds` parameter like other methods do. However,
[MySQL2Adapter's `exec_query`](https://github.com/rails/rails/blob/74a527cc63ef56f3d0a42cf638299958dc7cb08c/activerecord/lib/active_record/connection_adapters/mysql2_adapter.rb#L228L231)
works exactly the same whether this parameters is passed or not, so the output
does not change:

```ruby
def exec_query(sql, name = 'SQL', binds = [])
  result = execute(sql, name)
  ActiveRecord::Result.new(result.fields, result.to_a)
end
```

- Remove un-needed require in AJ rescue test.

Mention `perform_now` in AJ base docs to specify how to immediately invoke a job [ci skip]

Enable emitting of warnings from ActiveJob tests.

Message on AR::UnknownAttributeError should include the class name of a record

This would be helpful if 2 models have an attribute that has a similar
name to the other. e.g:

before:

    User.new(name: "Yuki Nishijima", projects_attributes: [name: "kaminari"])
    # => ActiveRecord::UnknownAttributeError: unknown attribute: name

after:

    User.new(name: "Yuki Nishijima", projects_attributes: [name: "kaminari"])
    # => ActiveRecord::UnknownAttributeError: unknown attribute on User: name

Merge branch 'activerecord-merge-docs' of https://github.com/justanshulsharma/rails into justanshulsharma-activerecord-merge-docs

remove duplicate method (_status_code) in action_dispatch

Fixed test throwing unused variable warning

Make status_at methods nodoc

- Also one minor change for documenting url_for method in ActionController::Metal.
[ci skip]

fix wrong example from #17318 [ci skip]

make guides example more friendly to nonlatin langs [ci skip]

[ci skip] add :queue option to deliver_later and deliver_later! documentation