[chore] [receiver/receivercreator] fix bad copypasta in test (createE…

…rr -> err) (open-telemetry#33808)

Chore/bugfix, goes from this

```
{"level":"error","ts":1719538225.8125398,"caller":"[email protected]/observerhandler.go:159","msg":"failed to start receiver","kind":"receiver","receiver":"jmx/cassandra","error":"failed starting endpoint-derived receiver: %!w(<nil>)",
```

to this


```
{"level":"error","ts":1719548614.7125309,"caller":"[email protected]/observerhandler.go:159","msg":"failed to start receiver","kind":"receiver","receiver":"jmx/cassandra","error":"failed starting endpoint-derived receiver: failed to parse Endpoint \"172.20.0.2:7199\": parse \"172.20.0.2:7199\": first path segment in URL cannot contain colon"
```

(fixing the issue with
[`url.Parse`](https://github.com/open-telemetry/opentelemetry-collector-contrib/blob/main/receiver/jmxreceiver/receiver.go#L174)
[error](https://github.com/golang/go/blob/master/src/net/url/url.go#L557)
is another topic entirely, given the jmx code accepts it without the
`jmx` prefix, but that's another issue...)

receiver/receivercreator/runner.go

@@ -108,7 +108,7 @@ func (run *receiverRunner) start(
 	}
 
 	if err = wr.Start(context.Background(), run.host); err != nil {
-		return nil, fmt.Errorf("failed starting endpoint-derived receiver: %w", createError)
+		return nil, fmt.Errorf("failed starting endpoint-derived receiver: %w", err)
 	}
 
 	return wr, nil