fix(test): flaky encryption

Minimal set of test reproduction:

```sh
COCKROACH_SKIP_LOAD_SCHEMA=1 SEED=13092 bundle exec rake test TESTOPTS="--name='/\A("\
"test_concurrent_insert_with_processes"\
"|test_uniqueness_validations_work_when_using_old_encryption_schemes"\
"|test_fixtures_get_encrypted_automatically"\
"|test_ciphertext_for_returns_the_ciphertext_of_a_value_when_the_record_is_new)\z/'"
```

It is important NOT TO run `ActiveRecord::Base.reset_column_information`.
Some tests are eagerly loading information to prevent side effects [^1].

We could run `Avenger.reset_column_information` but we actually do not
need it here.

[^1]: See https://github.com/rails/rails/blob/v8.1.1/activerecord/test/cases/encryption/helper.rb#L115-L120

Author: BuonOmo

test/cases/transactions_test.rb

@@ -18,13 +18,18 @@ def validate_unique_username
       end
     end
 
-    def test_concurrent_insert_with_processes
-      conn = ActiveRecord::Base.lease_connection
-      conn.create_table :avengers, force: true do |t|
+    def setup
+      @conn = ActiveRecord::Base.lease_connection
+      @conn.create_table :avengers, force: true do |t|
         t.string :name
       end
-      ActiveRecord::Base.reset_column_information
+    end
+
+    def teardown
+      @conn.drop_table :avengers, if_exists: true
+    end
 
+    def test_concurrent_insert_with_processes # corrupting #1
       avengers = %w[Hulk Thor Loki]
       Avenger.cyclic_barrier = Concurrent::CyclicBarrier.new(avengers.size - 1)
       Thread.current[:name] = "Main" # For debug logs.
@@ -41,8 +46,6 @@ def test_concurrent_insert_with_processes
       assert_equal avengers.size, Avenger.count
     ensure
       Thread.current[:name] = nil
-      conn = ActiveRecord::Base.lease_connection
-      conn.drop_table :avengers, if_exists: true
     end
   end
 end