Allow CTEs in read-only query with postgresql

Update Welcome Aboard text in Guides [ci skip]

Update `rails server` terminal output in Guides [ci skip]

Refactor `association.scoping` not to rely on `klass.all`

Avoid LazilyDefinedAttributes being included multiple times in class, and remove methods after first use

Fix Railties test suite for Sprockets 4.0

Fix new instance creation on association relation to respect unscope

activerecord: fix some test failers caused by recent backports

Since 8297f8a3, a test fails for 6-0-stable, fixed here. In master this
is not necessary because this whole ignoring has been removed.

Fixes some warning caused by the recent minitest upgrade backport.
The fixed code doesn't exist anymore in master, so it was missed.

Enumerator should be supported by ActiveSupport::SafeBuffer

Fixed performance regression introduced MySQL 8.0

test: fix tests after minitest upgrade

Fixes fallout from e01bf7f8. One `must_be_like` was missed.

Fix an issue with duplicate preloaded records

Address to the warning "DEPRECATED: global use of assertion methods"

Follow up of #37434.

Fix eager load for no :has_many with limit and joins for :has_many

Fix autosave validation context regression

Merge pull request #37353 from lxxxvi/correct-information-about-record-identification-for-form-helper

correct information about record identification in form helper [ci skip]

Deprecate leaking scope in callback block for association relation

Maintain extra joins for string or complex arel conditions

Backport #37228 and #37112 to 6-0-stable

Delay ActionDispatch::Response configuration to load-time

Allow ActionDispatch::Response to be autoloaded

Include connection in cached query notifications

Rational values are move precise than float values so when comparing
rationals values may be off by a few units that are hard to assert
equality. Let's make sure we are comparing the float value with float
values.

Define the `url_options` needed for SytemTest inside the route proxy:

Don't include routes helpers inside System test class:

Inherit from ActiveSupport::TestCase instead of ActionDispatch::IntegrationTest. Active Job automatically mixes its test helper into the latter, forcibly setting the test queue adapter before Capybara starts its app server.

As a bonus, we no longer need to remove the parts of the ActionDispatch::IntegrationTest API we don’t want to expose.

We were using picoseconds as precision but some Ruby implementations
only support up to nanoseconds. Since that much precision was not needed
to test the feature I decreased the precision.