fix: first_aired nullish for episode schema

Author: michaldrabik

projects/api/src/contracts/_internal/response/episodeResponseSchema.ts

@@ -6,7 +6,7 @@ export const episodeResponseSchema = z.object({
   season: z.number().int(),
   number: z.number().int(),
   title: z.string(),
-  first_aired: z.string(),
+  first_aired: z.string().nullish(),
   number_abs: z.number().int().nullish(),
   /***
    * Available if requesting extended `full`.