fix: change error to debug

[gruberb]

Description

When a double echo message (READY | ECHO) is received from a non-validator (a node which is not part of the validator list), it's technically not an error. It's expected behaviour. So we change it to debug instead of error so we don't overcrowd our logs.

PR Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added or updated tests that comprehensively prove my change is effective or that my feature works