Issue #3230668: Split out Composer Stager wiring into Package Manager submodule

tests/src/Kernel/ReadinessValidation/ComposerExecutableValidatorTest.php

@@ -20,7 +20,10 @@ class ComposerExecutableValidatorTest extends KernelTestBase {
   /**
    * {@inheritdoc}
    */
-  protected static $modules = ['automatic_updates'];
+  protected static $modules = [
+    'automatic_updates',
+    'package_manager',
+  ];
 
   /**
    * Tests that an error is raised if the Composer executable isn't found.