Set serverlessFunctionLayerId not nullable (#15272)

As title

Existing Null serverlessFunctionLayerIds have been filled with
`upgrade:1-8:fill-null-serverless-function-layer-id` command

See 0 such records in production

<img width="651" height="415" alt="image"
src="https://github.com/user-attachments/assets/9a5868fe-aa8e-4de0-b656-2e732560fd47"
/>

packages/twenty-server/src/engine/metadata-modules/serverless-function/serverless-function.entity.ts

@@ -68,8 +68,7 @@ export class ServerlessFunctionEntity
   @Column({ nullable: true, type: 'text' })
   checksum: string | null;
 
-  // TODO: should be set to nullable: false when 1.8 released in production
-  @Column({ nullable: true, type: 'uuid' })
+  @Column({ nullable: false, type: 'uuid' })
   serverlessFunctionLayerId: string;
 
   @ManyToOne(