Make sure we are using the correct connection pool when dumping the schema (rails#52777)

* Add test to make sure the schemas are different

Related to rails#52776.

Those two schemas files should be different,
as they are generated from different migrations.

* Make sure we are using the correct connection pool when dumping the schema

This was broken by 175bf82.

Before we were switching the connection pool to use the one for the
correspondent db config, but since we moved the `dump_schema` call to
outside of the `with_temporary_pool` block, we were using the default
connection pool.

Fixes rails#52776.

Author: rafaelfranca

activerecord/lib/active_record/tasks/database_tasks.rb

@@ -211,7 +211,9 @@ def prepare_all
         # Dump schema for databases that were migrated.
         if ActiveRecord.dump_schema_after_migration
           dump_db_configs.each do |db_config|
-            dump_schema(db_config)
+            with_temporary_pool(db_config) do
+              dump_schema(db_config)
+            end
           end
         end
 

railties/test/application/rake/multi_dbs_test.rb

@@ -598,11 +598,17 @@ class ThreeMigration < ActiveRecord::Migration::Current
         require "#{app_path}/config/environment"
         app_file "db/migrate/01_one_migration.rb", <<-MIGRATION
           class OneMigration < ActiveRecord::Migration::Current
+            def change
+              create_table :posts
+            end
           end
         MIGRATION
 
         app_file "db/animals_migrate/02_two_migration.rb", <<-MIGRATION
           class TwoMigration < ActiveRecord::Migration::Current
+            def change
+              create_table :dogs
+            end
           end
         MIGRATION
 
@@ -616,6 +622,8 @@ class TwoMigration < ActiveRecord::Migration::Current
           assert File.exist?("db/schema.rb")
           assert File.exist?("db/animals_schema.rb")
 
+          assert_not_equal File.read("db/schema.rb"), File.read("db/animals_schema.rb")
+
           primary_mtime = File.mtime("db/schema.rb")
           animals_mtime = File.mtime("db/animals_schema.rb")
         end