Log with lower severity when resources.json is not found

Export server version: v5.0.0
Highcharts version: 10.2.1

**Configuration:**
- `CUSTOM_LOGIC_ALLOW_CODE_EXECUTION = true` (code execution is allowed to support passing JS functions to formatters)
- `--enableServer 1` (as was already mentioned in https://github.com/highcharts/node-export-server/issues/451#issuecomment-2008524099, setting env variable `SERVER_ENABLE` does not work and it has to be passed as parameter in ENTRYPOINT)

**Current behaviour:**
When code execution is allowed, the server assumes that there should be `resources.json` file and if there is none, it issues a warning.

**Expected behaviour:**
Server does not log message with warning severity.

**Export server logs:**
```text
2025-04-05 14:52:14 Sat Apr 05 2025 12:52:14 GMT+0000 [warning] - [chart] Unable to load the default resources.json file.
```