fix: display leap year birthdays on the day following non-leap year #1087

[Serunthi]

Type of change(s)

• Bug fix
• Feature / enhancement
• Infrastructure / tooling (CI, build, deps, tests)
• Documentation

What changed and why

• Contact birthdays set on Feb 29 (leap day) were not displayed in non-leap years, causing them to appear only once every 4 years.
• Modified addYearsWithSameDay() in Event.kt to display leap day events on March 1st in non-leap years, and on Feb 29 in leap years.

Tests performed

• Created a contact with a birthday on Feb 29, 2024
• Imported birthdays into Fossify Calendar.
• Verified the birthday now appears on March 1st in non-leap years (2025, 2026, 2027)
• Verified the birthday still appears on Feb 29 in leap years ( 2028 )
• Tested on emulator Pixel 7

Before & after preview

Closes the following issue(s)

• Closes Contact Leap Birthdays not shown in off-years #1087

Checklist

• I read the contribution guidelines.
• I manually tested my changes on device/emulator (if applicable).
• I updated the "Unreleased" section in CHANGELOG.md (if applicable).
• I have self-reviewed my pull request (no typos, formatting errors, etc.).
• I understand every change in this pull request.