Merge pull request #14231 from brianstorti/bs-docs-secret-token

Use secrets.yml instead of secret_token.rb in the docs
Merge pull request #14226 from senny/14109_partial_revert

`includes` uses SQL parsing when String joins are involved.
Improve a bit the 4.1 release notes [ci skip]

Fix a few typos. #present_in has been changed to #presence_in through
commit d61baee5.
[ci skip] correct select examples and doc, ref [522c0fd]
Merge pull request #14230 from kuldeepaggarwal/doc-select

Correct `select` examples and doc, ref [522c0fd] [ci skip]
Improve collision explanation for Hash#transform_keys.

Based on comments at
https://github.com/rails/docrails/commit/42417b0013819e573be9ffc5402e179003156e8e#commitcomment-5527251

[skip ci]
set the error callback to a nice default in case nobody set an error callback and an error happens
[ci skip] use secrets.secret_key_base instead of config.secret_key_base
use secrets.yml instead of secret_token.rb
Merge pull request #14233 from kuldeepaggarwal/fix-secrets-doc

use `secrets.secret_key_base` instead of `config.secret_key_base`
Remove unnecessary db call when replacing.

When replacing a has_many association with the same one, there is no
need to do a round-trip to the db to create/and drop a new transaction.

[fixes #14220]
live controllers should have live responses

detect the type of controller we're testing and return the right type of
response based on that controller.  This allows us to stop doing the
weird sleep thing.
use built-in exception handling in live controllers

when an exception happens in an action before the response has been
committed, then we should re-raise the exception in the main thread.
This lets us reuse the existing exception handling.
Merge pull request #14195 from robin850/issue-14079

Avoid namespacing routes inside engines
make sure we wait for the threads to shut down before asserting closure
Replace map.flatten(1) with flat_map
Merge pull request #14240 from sferik/flat_map

Replace map.flatten(1) with flat_map
Merge pull request #14234 from arthurnn/fix_trans_on_replace

Remove unnecessary db call when replacing.
Refactor tests from BaseRackTest into BaseRequestTest
Fix warnings due to:
- unused variable in PG Adapter.
- Ambiguous argument warning from range_test for use - to + Infinity range without brackets.
Merge pull request #14248 from vipulnsward/fix-pg-ar-warnings

Fix PG warnings.