docs: fix outdated url (#26616)

Author: kaisnb

src/cdk/a11y/a11y.md

@@ -60,7 +60,7 @@ Each item must also have an ID bound to the listbox's or menu's `aria-activedesc
 
 The `cdkTrapFocus` directive traps <kbd>Tab</kbd> key focus within an element. This is intended to
 be used to create accessible experience for components like
-[modal dialogs](https://www.w3.org/TR/wai-aria-practices-1.1/#dialog_modal), where focus must be
+[modal dialogs](https://www.w3.org/WAI/ARIA/apg/patterns/dialog-modal/), where focus must be
 constrained.
 
 This directive is declared in `A11yModule`.

src/cdk/a11y/focus-trap/focus-trap.md

@@ -2,7 +2,7 @@
 
 The `cdkTrapFocus` directive traps <kbd>Tab</kbd> key focus within an element. This is intended to
 be used to create accessible experience for components like
-[modal dialogs](https://www.w3.org/TR/wai-aria-practices-1.1/#dialog_modal), where focus must be
+[modal dialogs](https://www.w3.org/WAI/ARIA/apg/patterns/dialog-modal/), where focus must be
 constrained.
 
 This directive is declared in `A11yModule`.