bug symfony#28524 [PhpUnitBridge] fix disabling DeprecationErrorHandler using phpunit.xml file (soerenbernstein)

This PR was submitted for the master branch but it was squashed and merged into the 3.4 branch instead (closes symfony#28524).

Discussion
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[PhpUnitBridge] fix disabling DeprecationErrorHandler using phpunit.xml file

Fixing symfony#28519

| Q             | A
| ------------- | ---
| Branch?       | master
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | don't know
| Fixed tickets | symfony#28519
| License       | MIT

Commits
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3cd929b [PhpUnitBridge] fix disabling DeprecationErrorHandler using phpunit.xml file

Author: nicolas-grekas

src/Symfony/Bridge/PhpUnit/DeprecationErrorHandler.php

@@ -54,7 +54,11 @@ public static function register($mode = 0)
             if (false === $mode) {
                 $mode = getenv('SYMFONY_DEPRECATIONS_HELPER');
             }
-            if (DeprecationErrorHandler::MODE_WEAK !== $mode && DeprecationErrorHandler::MODE_WEAK_VENDORS !== $mode && (!isset($mode[0]) || '/' !== $mode[0])) {
+            if (DeprecationErrorHandler::MODE_DISABLED !== $mode
+                && DeprecationErrorHandler::MODE_WEAK !== $mode
+                && DeprecationErrorHandler::MODE_WEAK_VENDORS !== $mode
+                && (!isset($mode[0]) || '/' !== $mode[0])
+            ) {
                 $mode = preg_match('/^[1-9][0-9]*$/', $mode) ? (int) $mode : 0;
             }