What is the ruling on lying to one's employer to justify an absence that was caused by attending another job interview, and am I sinful for that?

The default ruling for lying is prohibition, unless it becomes the only means to avert harm or restore a right. Allah and His Messenger have clarified the prohibition of lying and that it is one of the causes for entering Hellfire. Therefore, the liar must repent and seek forgiveness. If it is possible to use equivocation (tawriya) or double entendre (ma'arid), there is latitude in them as an alternative to lying.