bug symfony#23952 [PhpUnitBridge] install PHPUnit 6 on PHP 7.2 (xabbuh)

This PR was merged into the 3.3 branch.

Discussion
----------

[PhpUnitBridge] install PHPUnit 6 on PHP 7.2

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | symfony#23943
| License       | MIT
| Doc PR        |

Commits
-------

30336ea install PHPUnit 6 on PHP 7.2

Author: fabpot

src/Symfony/Bridge/PhpUnit/CHANGELOG.md

@@ -1,6 +1,11 @@
 CHANGELOG
 =========
 
+3.4.0
+-----
+
+ * PHPUnit 6 is installed when using PHP 7.2+
+
 3.3.0
 -----
 

src/Symfony/Bridge/PhpUnit/bin/simple-phpunit

@@ -15,8 +15,17 @@
 
 error_reporting(-1);
 
-// PHPUnit 4.8 does not support PHP 7, while 5.1 requires PHP 5.6+
-$PHPUNIT_VERSION = PHP_VERSION_ID >= 50600 ? getenv('SYMFONY_PHPUNIT_VERSION') ?: '5.7' : '4.8';
+if (PHP_VERSION_ID >= 70200) {
+    // PHPUnit 6 is required for PHP 7.2+
+    $PHPUNIT_VERSION = getenv('SYMFONY_PHPUNIT_VERSION') ?: '6.3';
+} elseif (PHP_VERSION_ID >= 50600) {
+    // PHPUnit 4 does not support PHP 7
+    $PHPUNIT_VERSION = getenv('SYMFONY_PHPUNIT_VERSION') ?: '5.7';
+} else {
+    // PHPUnit 5.1 requires PHP 5.6+
+    $PHPUNIT_VERSION = '4.8';
+}
+
 $oldPwd = getcwd();
 $PHPUNIT_DIR = getenv('SYMFONY_PHPUNIT_DIR') ?: (__DIR__.'/.phpunit');
 $PHP = defined('PHP_BINARY') ? PHP_BINARY : 'php';