fix(material/datepicker): incorrect year count in aria label (#22763)

Fixes that the `aria-label` of the navigation buttons in the year view said "20 years", even though we're showing 24 years.

Fixes #22758.

(cherry picked from commit f3c3096)

Author: crisbeto

src/material/datepicker/datepicker-intl.ts

@@ -41,10 +41,10 @@ export class MatDatepickerIntl {
   nextYearLabel: string = 'Next year';
 
   /** A label for the previous multi-year button (used by screen readers). */
-  prevMultiYearLabel: string = 'Previous 20 years';
+  prevMultiYearLabel: string = 'Previous 24 years';
 
   /** A label for the next multi-year button (used by screen readers). */
-  nextMultiYearLabel: string = 'Next 20 years';
+  nextMultiYearLabel: string = 'Next 24 years';
 
   /** A label for the 'switch to month view' button (used by screen readers). */
   switchToMonthViewLabel: string = 'Choose date';