Reset primary key sequence in FixturesResetPkSequenceTests

The primary key sequence for each test in FixturesResetPkSequenceTest is
reset.

The state in some of the FixturesResetPkSequenceTest tests are leaking,
causing failurse in others. Using a seed of `48104`, the
`FixturesResetPkSequenceTest#test_resets_to_min_pk_with_specified_pk_and_sequence`
runs before the `DatabaseStatementsTest` tests, and
the tests fail with duplicate primary key errors:

```
Run options: --seed 48104 -n
"/^(?:FixturesResetPkSequenceTest#(?:test_resets_to_min_pk_with_specified_pk_and_sequence)|DatabaseStatementsTest#(?:test_create_should_return_the_inserted_id|test_exec_insert|test_insert_should_return_the_inserted_id))$/"

.EEE

  1) Error:
DatabaseStatementsTest#test_exec_insert:
ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate
key value violates unique constraint "accounts_pkey"
DETAIL:  Key (id)=(2) already exists.

  2) Error:
DatabaseStatementsTest#test_create_should_return_the_inserted_id:
ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate
key value violates unique constraint "accounts_pkey"
DETAIL:  Key (id)=(3) already exists.

  3) Error:
DatabaseStatementsTest#test_insert_should_return_the_inserted_id:
ActiveRecord::RecordNotUnique: PG::UniqueViolation: ERROR:  duplicate
key value violates unique constraint "accounts_pkey"
DETAIL:  Key (id)=(4) already exists.
```

activerecord/test/cases/fixtures_test.rb

@@ -365,6 +365,7 @@ if Account.connection.respond_to?(:reset_pk_sequence!)
   class FixturesResetPkSequenceTest < ActiveRecord::TestCase
     fixtures :accounts
     fixtures :companies
+    self.use_transactional_tests = false
 
     def setup
       @instances = [Account.new(credit_limit: 50), Company.new(name: "RoR Consulting"), Course.new(name: "Test")]