Managed to reproduce CI failure at https://buildkite.com/rails/rails/builds/79496#0c03f856-9be1-4ca0-88c9-e1df21ae0a07

This commitaddresses the following errors by loading :author_addresses fixture because
`:authors` has a foreign key to `:author_addresses`.

* sqlite3 adapter
```ruby
$ bin/test test/cases/adapters/sqlite3/explain_test.rb test/cases/fixtures_test.rb -n "/^(?:SQLite3ExplainTest#(?:test_explain_with_eager_loading)|FixturesWithForeignKeyViolationsTest#(?:test_does_not_raise_if_no_fk_violations))$/" --seed 2529
Using sqlite3
Run options: -n "/^(?:SQLite3ExplainTest#(?:test_explain_with_eager_loading)|FixturesWithForeignKeyViolationsTest#(?:test_does_not_raise_if_no_fk_violations))$/" --seed 2529

.E

Error:
FixturesWithForeignKeyViolationsTest#test_does_not_raise_if_no_fk_violations:
RuntimeError: Foreign key violations found in your fixture data. Ensure you aren't referring to labels that don't exist on associations.
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:641:in `block in insert'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:629:in `each'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:629:in `insert'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:615:in `read_and_insert'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:567:in `create_fixtures'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:844:in `block (2 levels) in test_does_not_raise_if_no_fk_violations'
    /home/yahonda/src/github.com/rails/rails/activesupport/lib/active_support/testing/assertions.rb:34:in `assert_nothing_raised'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:843:in `block in test_does_not_raise_if_no_fk_violations'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:857:in `with_verify_foreign_keys_for_fixtures'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:842:in `test_does_not_raise_if_no_fk_violations'

bin/test test/cases/fixtures_test.rb:835

Finished in 0.045767s, 43.6991 runs/s, 174.7966 assertions/s.
2 runs, 8 assertions, 0 failures, 1 errors, 0 skips
$
```

* postgresql adapter

```ruby
$ ARCONN=postgresql bin/test test/cases/adapters/postgresql/explain_test.rb test/cases/fixtures_test.rb -n "/^(?:PostgreSQLExplainTest#(?:test_explain_with_eager_loading)|FixturesWithForeignKeyViolationsTest#(?:test_does_not_raise_if_no_fk_violations))$/" --seed 16926
Using postgresql
Run options: -n "/^(?:PostgreSQLExplainTest#(?:test_explain_with_eager_loading)|FixturesWithForeignKeyViolationsTest#(?:test_does_not_raise_if_no_fk_violations))$/" --seed 16926

.E

Error:
FixturesWithForeignKeyViolationsTest#test_does_not_raise_if_no_fk_violations:
RuntimeError: Foreign key violations found in your fixture data. Ensure you aren't referring to labels that don't exist on associations.
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:641:in `block in insert'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:629:in `each'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:629:in `insert'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:615:in `read_and_insert'
    /home/yahonda/src/github.com/rails/rails/activerecord/lib/active_record/fixtures.rb:567:in `create_fixtures'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:844:in `block (2 levels) in test_does_not_raise_if_no_fk_violations'
    /home/yahonda/src/github.com/rails/rails/activesupport/lib/active_support/testing/assertions.rb:34:in `assert_nothing_raised'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:843:in `block in test_does_not_raise_if_no_fk_violations'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:857:in `with_verify_foreign_keys_for_fixtures'
    /home/yahonda/src/github.com/rails/rails/activerecord/test/cases/fixtures_test.rb:842:in `test_does_not_raise_if_no_fk_violations'

bin/test test/cases/fixtures_test.rb:835

Finished in 0.121193s, 16.5027 runs/s, 49.5080 assertions/s.
2 runs, 6 assertions, 0 failures, 1 errors, 0 skips
$
```

* It does not reproduce with mysql2 adapter because MySQL does not have
  features to validate existing foreign keys, but added
  :author_addresses in Mysql2ExplainTest for consistency.

Follow up #42674