bug #36566 [PhpUnitBridge] Use COMPOSER_BINARY env var if available (fancyweb)

This PR was merged into the 3.4 branch.

Discussion
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[PhpUnitBridge] Use COMPOSER_BINARY env var if available

| Q             | A
| ------------- | ---
| Branch?       | 3.4
| Bug fix?      | yes
| New feature?  | no
| Deprecations? | no
| Tickets       | symfony/symfony#36401
| License       | MIT
| Doc PR        | -

Commits
-------

6dce90d47b [PhpUnitBridge] Use COMPOSER_BINARY env var if available

Author: fabpot

bin/simple-phpunit

@@ -65,11 +65,13 @@ foreach ($defaultEnvs as $envName => $envValue) {
     }
 }
 
-$COMPOSER = file_exists($COMPOSER = $oldPwd.'/composer.phar')
-    || ($COMPOSER = rtrim('\\' === DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer.phar`) : `which composer.phar 2> /dev/null`))
-    || ($COMPOSER = rtrim('\\' === DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer`) : `which composer 2> /dev/null`))
-    ? (file_get_contents($COMPOSER, false, null, 0, 18) === '#!/usr/bin/env php' ? $PHP : '').' '.escapeshellarg($COMPOSER) // detect shell wrappers by looking at the shebang
-    : 'composer';
+if (false === $COMPOSER = \getenv('COMPOSER_BINARY')) {
+    $COMPOSER = file_exists($COMPOSER = $oldPwd.'/composer.phar')
+        || ($COMPOSER = rtrim('\\' === DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer.phar`) : `which composer.phar 2> /dev/null`))
+        || ($COMPOSER = rtrim('\\' === DIRECTORY_SEPARATOR ? preg_replace('/[\r\n].*/', '', `where.exe composer`) : `which composer 2> /dev/null`))
+        ? (file_get_contents($COMPOSER, false, null, 0, 18) === '#!/usr/bin/env php' ? $PHP : '').' '.escapeshellarg($COMPOSER) // detect shell wrappers by looking at the shebang
+        : 'composer';
+}
 
 if (false === $SYMFONY_PHPUNIT_REMOVE = getenv('SYMFONY_PHPUNIT_REMOVE')) {
     $SYMFONY_PHPUNIT_REMOVE = 'phpspec/prophecy symfony/yaml';