Fix errbit error state pension topup

- Fixed rates not being shown for certain birthdays for women.
- For birthdays which fall on the 29th February in a leap year the calculator shifts their birthday to the 1st March for the purposes of finding the correct rate. This was previously throwing an error.
- Shifting the date forward by one day is similar to what the calculate-state-pension tool does.

https://www.agileplannerapp.com/boards/105200/cards/6143