"Cannot read property 'length' of undefined" error when there is no message is SQS queue

Hi :)

When calling the `getEvents` and that no message is present in the queue (because no events made is to EventBridge), instead of returning an empty array, or throwing a clear exception, I get:

```
TypeError: Cannot read property 'length' of undefined
at EventBridge.getEvents (/Users/georgesbiaux/Projects/Pyxo/pyxo/backend/node_modules/sls-test-tools/lib/helpers/eventBridge.js:101:25)
at processTicksAndRejections (internal/process/task_queues.js:93:5)
at Function.getAllEventBridgeMessages (/Users/georgesbiaux/Projects/Pyxo/pyxo/backend/tests/functions/utils/event-bridge.utils.ts:76:24)
at Object. (/Users/georgesbiaux/Projects/Pyxo/pyxo/backend/tests/functions/deposit/createDepositCommand.test.ts:128:7)
```

When my test suite fails because an event has not been send correctly to EventBridge, it would be clearer if it was the assertion on the event that cause the failure :)

Thanks