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

tests/src/Kernel/ReadinessValidation/ComposerExecutableValidatorTest.php

@@ -141,7 +141,7 @@ class ComposerExecutableValidatorTest extends KernelTestBase {
         // recognized, supported version number out of this output.
         $validator($validator::OUT, "Composer version $reported_version");
       });
-    $this->container->set('automatic_updates.composer_runner', $runner->reveal());
+    $this->container->set('package_manager.composer_runner', $runner->reveal());
 
     // If the validator can't find a recognized, supported version of Composer,
     // it should produce errors.