improve error message if a migration contains the old base migration class

[LordSimal]

Fixes #1058

Now PHPUnit fails with this error:

PHPUnit 13.0.5 by Sebastian Bergmann and contributors.

Error in bootstrap script: RuntimeException:
Could not apply migrations for {"connection":"test"}

Migrations failed to apply with message:

Migration file `/Users/kevin/Documents/sunlime/alfred/config/Migrations/20260311200000_Initial.php` uses the legacy `Migrations\AbstractMigration` class, which is not available in this version. Update the migration to extend `Migrations\BaseMigration`.

If you are using the `skip` option and running multiple sets of migrations on the same connection, you can't skip tables managed by CakePHP in the connection.
#0 /Users/kevin/Documents/sunlime/alfred/tests/bootstrap.php(62): Migrations\TestSuite\Migrator->runMany(Array)
#1 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/src/TextUI/Configuration/BootstrapLoader.php(61): include_once('/Users/kevin/Do...')
#2 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/src/TextUI/Configuration/BootstrapLoader.php(36): PHPUnit\TextUI\Configuration\BootstrapLoader->load('/Users/kevin/Do...')
#3 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/src/TextUI/Application.php(132): PHPUnit\TextUI\Configuration\BootstrapLoader->handle(Object(PHPUnit\TextUI\Configuration\Configuration))
#4 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/phpunit(104): PHPUnit\TextUI\Application->run(Array)
#5 /Users/kevin/Documents/sunlime/alfred/vendor/bin/phpunit(122): include('/Users/kevin/Do...')
#6 {main}

Previous error: RuntimeException:
Migration file `/Users/kevin/Documents/sunlime/alfred/config/Migrations/20260311200000_Initial.php` uses the legacy `Migrations\AbstractMigration` class, which is not available in this version. Update the migration to extend `Migrations\BaseMigration`.
#0 /Users/kevin/Documents/sunlime/alfred/vendor/cakephp/migrations/src/Migration/Manager.php(978): Migrations\Migration\Manager->checkMigrationClass('/Users/kevin/Do...')
#1 /Users/kevin/Documents/sunlime/alfred/vendor/cakephp/migrations/src/Migration/Manager.php(452): Migrations\Migration\Manager->getMigrations()
#2 /Users/kevin/Documents/sunlime/alfred/vendor/cakephp/migrations/src/Migration/BuiltinBackend.php(96): Migrations\Migration\Manager->migrate(NULL)
#3 /Users/kevin/Documents/sunlime/alfred/vendor/cakephp/migrations/src/Migrations.php(114): Migrations\Migration\BuiltinBackend->migrate(Array)
#4 /Users/kevin/Documents/sunlime/alfred/vendor/cakephp/migrations/src/TestSuite/Migrator.php(116): Migrations\Migrations->migrate(Array)
#5 /Users/kevin/Documents/sunlime/alfred/tests/bootstrap.php(62): Migrations\TestSuite\Migrator->runMany(Array)
#6 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/src/TextUI/Configuration/BootstrapLoader.php(61): include_once('/Users/kevin/Do...')
#7 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/src/TextUI/Configuration/BootstrapLoader.php(36): PHPUnit\TextUI\Configuration\BootstrapLoader->load('/Users/kevin/Do...')
#8 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/src/TextUI/Application.php(132): PHPUnit\TextUI\Configuration\BootstrapLoader->handle(Object(PHPUnit\TextUI\Configuration\Configuration))
#9 /Users/kevin/Documents/sunlime/alfred/vendor/phpunit/phpunit/phpunit(104): PHPUnit\TextUI\Application->run(Array)
#10 /Users/kevin/Documents/sunlime/alfred/vendor/bin/phpunit(122): include('/Users/kevin/Do...')
#11 {main}