Revert "Do not swallow exceptions in event subscribers when PHPUnit's own test suite is running"

This reverts commit aae2542.

Author: sebastianbergmann

src/Event/Dispatcher/DirectDispatcher.php

@@ -11,7 +11,6 @@
 
 use const PHP_EOL;
 use function array_key_exists;
-use function defined;
 use function dirname;
 use function sprintf;
 use function str_starts_with;
@@ -115,8 +114,7 @@ public function dispatch(Event $event): void
      */
     public function handleThrowable(Throwable $t): void
     {
-        if (!defined('PHPUNIT_TESTSUITE') &&
-            $this->isThrowableFromThirdPartySubscriber($t)) {
+        if ($this->isThrowableFromThirdPartySubscriber($t)) {
             Facade::emitter()->testRunnerTriggeredPhpunitWarning(
                 sprintf(
                     'Exception in third-party event subscriber: %s%s%s',