title: Angular Material DatePicker disable days not working correctly
body: <p>I am using Angular material datepicker (V 9.2.4) and have problems to disable the date (day) selection. Even in the example for the datepicker that allows only year and month selection (see at <a href="https://stackblitz.com/angular/rejxkojdell?file=src%2Fapp%2Fdatepicker-views-selection-example.ts" rel="noreferrer">official datepicker example with only year and month selection</a>) it does not work. It works, when you select a year in the list under the dropdown component with years. After having selected a year, you will see the month selection and after having selected a month, the datepicker closes. But if you click onto the dropdown list for years (marked with the red arrow in my first screenshot), it doesn't (see pictures).</p>
  <p><a href="https://i.stack.imgur.com/FtrSx.png" rel="noreferrer"><img src="https://i.stack.imgur.com/FtrSx.png" alt="Year selection dropdown" /></a> <a href="https://i.stack.imgur.com/GPGb3.png" rel="noreferrer"><img src="https://i.stack.imgur.com/GPGb3.png" alt="day selection" /></a></p>
  <p>Is there any way to disable the date (day) selection? In my case I need this as the service behind only needs the month and year selection. The application sets the day on my side automatically to 1 and if a user could select a day, it would be confusing.</p>