fix(material/datepicker): resolve repeater warnings in calendar

Fixes that the calendar was triggering some newly-introduced warnings from the framework.

Fixes #29008.

Author: crisbeto

src/material/datepicker/calendar-body.html

@@ -14,7 +14,7 @@
 }
 
 <!-- Create the first row separately so we can include a special spacer cell. -->
-@for (row of rows; track row; let rowIndex = $index) {
+@for (row of rows; track rowIndex; let rowIndex = $index) {
   <tr role="row">
     <!--
       This cell is purely decorative, but we can't put `aria-hidden` or `role="presentation"` on it,
@@ -36,7 +36,7 @@
       cell is interactable, as well as the selection state via `aria-pressed`. See #23476 for
       background.
     -->
-    @for (item of row; track item; let colIndex = $index) {
+    @for (item of row; track colIndex; let colIndex = $index) {
       <td
         role="gridcell"
         class="mat-calendar-body-cell-container"

src/material/datepicker/month-view.html

@@ -1,7 +1,7 @@
 <table class="mat-calendar-table" role="grid">
   <thead class="mat-calendar-table-header">
     <tr>
-      @for (day of _weekdays; track day) {
+      @for (day of _weekdays; track $index) {
         <th scope="col">
           <span class="cdk-visually-hidden">{{day.long}}</span>
           <span aria-hidden="true">{{day.narrow}}</span>