[MaterialDatePicker] Update elevation to match specs

Resolves #2987

PiperOrigin-RevId: 490248736

Author: paulfthomas

lib/java/com/google/android/material/datepicker/res/values/dimens.xml

@@ -77,6 +77,6 @@
   <!-- only portrait and screens with less than 360dp minimum dimension-->
   <dimen name="mtrl_calendar_days_of_week_height">24dp</dimen>
 
-  <dimen name="m3_datepicker_elevation">@dimen/m3_sys_elevation_level1</dimen>
+  <dimen name="m3_datepicker_elevation">@dimen/m3_sys_elevation_level3</dimen>
 
 </resources>