Issue #3338789: Recurring random failure in caused by "PHP temp directory (/tmp) does not exist or is not writable to Composer." in kernel tests

package_manager/src/Validator/ComposerPluginsValidator.php

@@ -175,6 +175,9 @@ final class ComposerPluginsValidator implements EventSubscriberInterface {
     }
 
     // Only packages with `true` as a value are actually executed by composer.
+    if (!is_array($value)) {
+      var_dump($value);
+    }
     assert(is_array($value));
     $allowed_plugins = array_keys(array_filter($value));
     // Normalized allowed plugins: keys are normalized package names, values are