Fix join table column quoting with SQLite.

Make AJ::Base#enqueue return false if the job wasn't enqueued

Update bundler to 2.0.0.pre.2

Add MailDeliveryJob for unified mail delivery

Since bd623893, isolate test of `test_serialized_attribute_works_under_concurrent_initial_access` fails.

```
$ ./bin/test -w test/cases/serialized_attribute_test.rb -n test_serialized_attribute_works_under_concurrent_initial_access
Using sqlite3
Run options: -n test_serialized_attribute_works_under_concurrent_initial_access --seed 32129

# Running:

E

Error:
SerializedAttributeTest#test_serialized_attribute_works_under_concurrent_initial_access:
ActiveRecord::StatementInvalid: SQLite3::SQLException: no such table:
```

If duplicate an unloaded model, it seems that method invocation for that class
is not guaranteed. Use the original class to avoid it.

Merge pull request #34620 from ysksn/use_safe_navigation_operator_for_railsguides_generator_constructor

Use String for direction of RailsGuides::Generator#new

Use String for direction of RailsGuides::Generator

Colorize the unpermitted params log message

Add advanced test helpers docs to guides

[ci skip]

Another Ruby 2.6 BigDecimal compatibility issue

Fix attribute decoration leak on serialized attribute test

Add note about symbols vs strings

Now it accepts the base release to be compared with.

[ci skip]

option to disable all scopes that `ActiveRecord.enum` generates

Add `MailDeliveryJob` for delivering both regular and parameterized mail.
Deprecate using `DeliveryJob` and `Parameterized::DeliveryJob`.

This patch modifies XmlMini::Parsing["decimal"] to handle a string that
contains an invalid number. Since [ruby/ruby@a0e438c#diff-6b866d482baf2bdfd8433893fb1f6d36R144](https://github.com/ruby/ruby/commit/a0e438cd3c28d2eaf4efa18243d5b6edafa14d88#diff-6b866d482baf2bdfd8433893fb1f6d36R144) this case raises an `ArgumentError`. `String.to_f` returns 0.0 if there is not a valid number at the start of the argument, so current behavior is conserved.

See https://travis-ci.org/rails/rails/jobs/463180341#L6264

Related: #34600, #34601

Ensure that `delete_all` on collection proxy returns affected count

Reset scope after collection delete

Unlike the `Relation#delete_all`, `delete_all` on collection proxy
doesn't return affected count. Since the `CollectionProxy` is a subclass
of the `Relation`, this inconsistency is probably not intended, so it
should return the count consistently.

Reset scope after delete on collection association to clear stale
offsets of removed records.

Improve parallel testing guide [ci skip]

Pass the `connection` to the `@instrumenter.instrument` method call

Fix NumericData.average test on 2.6.0-dev

And hide the `READ_QUERY` internal constant.

- Fix formatting
- Don't repeat "Active Record automatically handles creating and migrating a new
  database for each worker to use."
- Tell that AR loads the schema to a database for each process(Related to #33479)
- Clarify that `parallelize_teardown` is executed for each process

Assigned but unused variable - bird

Add missing authorship to ActionCable changelog entry

I accidentally forgot to add the author line to my changelog entry from
2bb4fdef

See: https://travis-ci.org/rails/rails/jobs/462233144#L1384