registration: Move 'TrackingCategories' to lazy-loaded attribute

This value is only needed in specific contexts, so it doesn't make sense
to be loaded/cached for every request during initialization.

Bug: T187154
Change-Id: Ic6e2a29373724a517d64030d5c7d54b3f6197fa0

includes/registration/ExtensionRegistry.php

@@ -57,6 +57,7 @@ class ExtensionRegistry {
 	 * Attributes that should be lazy-loaded
 	 */
 	private const LAZY_LOADED_ATTRIBUTES = [
+		'TrackingCategories',
 		'QUnitTestModules',
 	];