fix typo in `assert_enqueued_jobs` example [ci skip]

MariaDB does not support JSON type

Referencing Rails.env without checking if it's defined couples
us to Railties.

Fix by avoiding the line breaks if we don't have an env check
to rely on.

Remove unused private method

Remove duplicated `require 'arel'`

Fixes #22980.

Replace old Rails greeting references

It appears first in `lib/active_record.rb`.

Revert "No need to specify Ruby patch version on Travis CI"

Revert "When generating a mailer, you must specify Mailer in the class name in"

A couple of the READMEs were still referring the old welcome page. This
is a small change that goes over it.

[ci skip]

This reverts commit 8417d967.

In 5697bdbb and af3eb596,
add mailer suffix to generated files and classes.
Therefore, no longer need to specify `Mailer` to class name. [ci skip]

Follow up of https://github.com/rails/rails/commit/c9feea6c9ab4494b0cb0b8cf4316847854f65af6

Previous commit accidentally broke mixing line filters with string -n filter.

Fix by checking if it is a string and returning it.

We also need to ensure the -n filter carry forward into any other composite filters.

Fix by letting the named filter be extractable, so we'll keep this for the next runnable's
run.

This reverts commit 99801c6a.

Ultimately it doesn't matter whether `add_index` or `t.index` are used
in the schema dumper in any meaningful way. There are gems out there
which hook into the old behavior for things like indexing materialized
views. Since the reverted commit doesn't seem to add much benefit,
there's no reason for us to break these gems.

No need to specify Ruby patch version on Travis CI

Travis CI now select the latest patch version of Ruby automatically when
given MAJOR.MINOR version string.

Tests can (and do) access the database from the main thread.  In this
case they were starting a transaction, then making a request.  The
request would create a new thread, which would allocate a new database
connection.  Since the main thread started a transaction that contains
data that the new thread wants to see, the new thread would not see it
due to data visibility from transactions.  Spawning the new thread in
production is fine because middleware should not be doing database
manipulation similar to the test harness.  Before 603fe20c it was
possible to set the database connection id based on a thread local, but
603fe20c changes the connection lookup code to never look at the
"connection id" but only at the thread object itself.  Without that
indirection, we can't force threads to use the same connection pool as
another thread.

Fixes #23483

When generating a mailer, you must specify Mailer in the class name

order to generate the proper files. Some of the docs/comments are
missing this important detail.

Update turbolinks-rails for passing railties test

don’t explicitly mention EventMachine [ci skip]

Follow up to 6accef4e

Ref - https://github.com/turbolinks/turbolinks-rails/pull/3

move CHANGELOG entry to the appropriate position [ci skip]

Dummy apple icon files has been added after the 5.0.0.beta2 release.
ref: #23455

add missing include to engine test example [ci skip]