Merge branch '3373589-deprecation-warnings-when' into '3.0.x'

Issue #3373589: Deprecation warnings when running PHP 8.2

See merge request !23

src/Annotation/InstallablePlugin.php

@@ -24,6 +24,11 @@ abstract class InstallablePlugin extends AnnotationObject {
    */
   public $libraries = [];
 
+  /**
+   * Internal marker to ensure required dependencies are enabled.
+   */
+  public $_requiredBy;
+
   /**
    * Retrieves the installed library or plugin identifier.
    *