Remove duplicate conditions in switch statement to fix build errors.

[Wataru343]

Hello,

I've made a small change to fix build errors caused by duplicate conditions in a switch statement. The errors were as follows:

SwiftDate/Sources/SwiftDate/Supports/Calendars.swift:86:8: error: Duplicate Conditions Violation: Duplicate sets of conditions in the same branch instruction should be avoided (duplicate_conditions)
SwiftDate/Sources/SwiftDate/Supports/Calendars.swift:87:8: error: Duplicate Conditions Violation: Duplicate sets of conditions in the same branch instruction should be avoided (duplicate_conditions)

To resolve these errors, I removed the duplicate case statements in the switch block.

Build environment Xcode: 14.3 macOS: 13.3