undefined method `safe_load' for Syck:Module

## Describe the bug
I have a `gem 'syck', "1.4.1"` gem. Everything works fine unless I add `gem 'elastic-apm', "4.7.2"`

## Steps to reproduce

## Expected behavior

## Environment

- **OS**:
Docker container
- **Ruby version**:
2.4.6
- **Framework and version**:
3.2.22.5
- **APM Server version**:
- **Agent version**:

## Additional context

Add any other context about the problem here.

- Agent config options

Click to expand

```
replace this line with your agent config options
remember to mask any sensitive fields like tokens
```