Fix invalid UUID insert in workflow core-links backfill (#23118)

## Fix invalid UUID insert in workflow core-links backfill

### Problem
The `2-23:backfill-workflow-core-links` workspace upgrade command failed
with:

```
QueryFailedError: invalid input syntax for type uuid: "" (22P02)
```

The `core."workflow"."lastPublishedVersionId"` column is a `uuid`, but
some workspace workflows store an empty string `""` (not `NULL`) for
that field. The code used `workflow.lastPublishedVersionId ?? null`, and
`??` only falls back on `null`/`undefined` — so `""` was passed straight
through and Postgres rejected it.

### Fix
Use `|| null` instead of `?? null` so empty strings are normalized to
`null` before insertion into the `uuid` column.


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packages/twenty-server/src/database/commands/upgrade-version-command/2-23/2-23-workspace-command-1784286707000-backfill-workflow-core-links.command.ts

@@ -110,7 +110,7 @@ export class BackfillWorkflowCoreLinksCommand extends ProvisionedWorkspaceComman
               uuidv4(),
               applicationId,
               workflow.name ?? null,
-              workflow.lastPublishedVersionId ?? null,
+              workflow.lastPublishedVersionId || null,
             ],
           );