This PR changes the text color of non-selectable days in the CupertinoDatePicker to match non-selectable months and years.

Current:
![Screenshot_1696829290](https://github.com/flutter/flutter/assets/147121557/209fee88-9efc-4b92-803a-453ecc6a7c16)

New:
![Screenshot_1696830232](https://github.com/flutter/flutter/assets/147121557/ecd11266-4c22-49cc-9bb5-2df39d10cf79)

Fixes #136179