Update autmoated testing configuration and fix broken 9.3.x tests

Problem/Motivation

The automated testing configuration for the 8.x-1.x branch of this project seems to have been disabled because it was configured to use Drupal 8.9.x. The status currently reads disabled, testing configuration no longer available

Additionally the default testing that is selected for new issue patches uses Drupal 9.3.x and some of the exosting automated tests are failing on Drupal core 9.3.x for every patch. Example failures:

exception: [Other] Line 0 of sites/default/files/simpletest/phpunit-2.xml:
PHPUnit Test failed to complete; Error: PHPUnit 8.5.21 by Sebastian Bergmann and contributors.

Testing Drupal\Tests\smtp\Unit\Plugin\Mail\SMTPMailSystemTest
...........EEEE                                                   15 / 15 (100%)

Time: 362 ms, Memory: 8.00 MB

There were 4 errors:

1) Drupal\Tests\smtp\Unit\Plugin\Mail\SMTPMailSystemTest::testMailValidator with data set "Without umlauts, Drupal mail validator, no exception" ('test@drupal.org', 'PhpUnit Localhost ', Drupal\Component\Utility\EmailValidator Object (...), null)
TypeError: Argument 1 passed to Egulias\EmailValidator\EmailValidator::isValid() must be of the type string, null given, called in /var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php on line 30

/var/www/html/vendor/egulias/email-validator/src/EmailValidator.php:35
/var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php:30
/var/www/html/modules/contrib/smtp/src/Plugin/Mail/SMTPMailSystem.php:258
/var/www/html/modules/contrib/smtp/tests/src/Unit/Plugin/Mail/SMTPMailSystemTest.php:273
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestResult.php:703
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/TextUI/TestRunner.php:656
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:235
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:194

2) Drupal\Tests\smtp\Unit\Plugin\Mail\SMTPMailSystemTest::testMailValidator with data set "With umlauts in local part, Drupal mail validator, no exception" ('testmüller@drupal.org', 'PhpUnit Localhost ', Drupal\Component\Utility\EmailValidator Object (...), null)
TypeError: Argument 1 passed to Egulias\EmailValidator\EmailValidator::isValid() must be of the type string, null given, called in /var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php on line 30

/var/www/html/vendor/egulias/email-validator/src/EmailValidator.php:35
/var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php:30
/var/www/html/modules/contrib/smtp/src/Plugin/Mail/SMTPMailSystem.php:258
/var/www/html/modules/contrib/smtp/tests/src/Unit/Plugin/Mail/SMTPMailSystemTest.php:273
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestResult.php:703
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/TextUI/TestRunner.php:656
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:235
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:194

3) Drupal\Tests\smtp\Unit\Plugin\Mail\SMTPMailSystemTest::testMailValidator with data set "With umlauts in domain part, Drupal mail validator, no exception" ('test@müllertest.de', 'PhpUnit Localhost ', Drupal\Component\Utility\EmailValidator Object (...), null)
TypeError: Argument 1 passed to Egulias\EmailValidator\EmailValidator::isValid() must be of the type string, null given, called in /var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php on line 30

/var/www/html/vendor/egulias/email-validator/src/EmailValidator.php:35
/var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php:30
/var/www/html/modules/contrib/smtp/src/Plugin/Mail/SMTPMailSystem.php:258
/var/www/html/modules/contrib/smtp/tests/src/Unit/Plugin/Mail/SMTPMailSystemTest.php:273
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestResult.php:703
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/TextUI/TestRunner.php:656
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:235
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:194

4) Drupal\Tests\smtp\Unit\Plugin\Mail\SMTPMailSystemTest::testMailValidator with data set "Without top-level domain in domain part, Drupal mail validator, no exception" ('test@drupal', 'PhpUnit Localhost ', Drupal\Component\Utility\EmailValidator Object (...), null)
TypeError: Argument 1 passed to Egulias\EmailValidator\EmailValidator::isValid() must be of the type string, null given, called in /var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php on line 30

/var/www/html/vendor/egulias/email-validator/src/EmailValidator.php:35
/var/www/html/core/lib/Drupal/Component/Utility/EmailValidator.php:30
/var/www/html/modules/contrib/smtp/src/Plugin/Mail/SMTPMailSystem.php:258
/var/www/html/modules/contrib/smtp/tests/src/Unit/Plugin/Mail/SMTPMailSystemTest.php:273
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestResult.php:703
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/Framework/TestSuite.php:627
/var/www/html/vendor/phpunit/phpunit/src/TextUI/TestRunner.php:656
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:235
/var/www/html/vendor/phpunit/phpunit/src/TextUI/Command.php:194

ERRORS!
Tests: 15, Assertions: 26, Errors: 4.

Steps to reproduce

• Add a patch to any issue using the default automated testing option (Drupal 9.3.x)
• See the same failures as below

Proposed resolution

• Enable periodic testing (and commit testing) with Drupal 9.3.x
• Fix (or temporarily disable) broken tests.

Remaining tasks

User interface changes

API changes

Data model changes