[BUG] - Program crashes if the day of the month is the 31st

[margual56]

Bug description

When setting the recurrence day of a subscription or income to be the 31st of a month, it crashes.

To Reproduce

1. Create a new monthly subscription
2. Set the recurrence day to 31
3. Save
4. The program crashes

Expected behavior

It should not crash. The 31st should be interpreted as "the last day of the month".

Screenshots

N/A

Information

• OS: N/A
• Program version: 0.1.2

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Additional context
A dropdown could also be added with the options "first day of the month", "last day of the month", etc.

Originally reported by @inoricat

[margual56]

The program assumes that "day 31" means whatever the last day of the month is for each month. Day 30 is just a recurrence on day 30 (or day 28 in February).

Waiting for feedback on this change.