[2.3.0] Checkmk Werk 16208 created: time_period: Fix error when updating a time period without changing its alias

Title: time_period: Fix error when updating a time period without changing its alias Class: fix Compatible: compat Component: rest-api Date: 1702559447 Edition: cre Level: 1 Version: 2.3.0b1 Prior to this Werk, when updating a time period keeping the same alias, it would raise an error due to the alias already being in use. This fix changes that and performs the requested update.