[Bug]: Deno.cron must be called at top-level only.

### Problem description

I have defined cron jobs in my app.ts, which is the entrypoint into the application. The cron jobs have worked for the past 2 months. Without having changed a single line in that file, I suddenly get the error

```
Deno.cron must be called at top-level only.
```

### Steps to reproduce

Define a cron job on top level.

### Expected behavior

No error

### Environment

Deno 1.45.5

### Possible solution

_No response_

### Additional context

_No response_