Reestablish connection to previous database after after running `db:schema:load:name`

After running `db:schema:load:name` the previous connection is restored.

Fixes #42912

activerecord/CHANGELOG.md

@@ -1,3 +1,9 @@
+*   Reestablish connection to previous database after after running `db:schema:load:name`
+
+    After running `db:schema:load:name` the previous connection is restored.
+
+    *Jacopo Beschi*
+
 *   Add database config option `database_tasks`
 
     If you would like to connect to an external database without any database

activerecord/lib/active_record/railties/databases.rake

@@ -493,8 +493,11 @@ db_namespace = namespace :db do
       ActiveRecord::Tasks::DatabaseTasks.for_each(databases) do |name|
         desc "Loads a database schema file (either db/schema.rb or db/structure.sql, depending on `config.active_record.schema_format`) into the #{name} database"
         task name => :load_config do
+          original_db_config = ActiveRecord::Base.connection_db_config
           db_config = ActiveRecord::Base.configurations.configs_for(env_name: ActiveRecord::Tasks::DatabaseTasks.env, name: name)
           ActiveRecord::Tasks::DatabaseTasks.load_schema(db_config, ActiveRecord.schema_format, ENV["SCHEMA"])
+        ensure
+          ActiveRecord::Base.establish_connection(original_db_config) if original_db_config
         end
       end
     end

railties/test/application/rake/multi_dbs_test.rb

@@ -475,6 +475,27 @@ module ApplicationTests
         end
       end
 
+      test "db:schema:load:name sets the connection back to its original state" do
+        Dir.chdir(app_path) do
+          dummy_task = <<~RUBY
+            task foo: :environment do
+              Book.first
+            end
+          RUBY
+          app_file("Rakefile", dummy_task, "a+")
+
+          generate_models_for_animals
+
+          rails("db:migrate:primary")
+
+          rails "db:migrate:animals", "db:schema:dump:animals"
+
+          assert_nothing_raised do
+            rails("db:schema:load:animals", "foo")
+          end
+        end
+      end
+
       test "db:migrate respects timestamp ordering across databases" do
         require "#{app_path}/config/environment"
         app_file "db/migrate/01_one_migration.rb", <<-MIGRATION