MDL-77348 mod_glossary: Added missing class properties

In PHP 8.2 and later, setting a value to an undeclared class property is
deprecated and emits a deprecation notice.
So we need to add missing class properties that still need to be declared.

mod/glossary/locallib.php

@@ -224,6 +224,9 @@ class glossary_entry_portfolio_caller extends portfolio_module_caller_base {
     /** @var array Array that contains all aliases for the given glossary entry. */
     private array $aliases = [];
 
+    /** @var array categories. */
+    private array $categories = [];
+
     /*
      * @return array
      */