refactor: Change logging level for missing attributes.

[FayeDel]

About

This pull request changes the logger level of missing attributes to DEBUG instead of INFO.
This is a necessary change as this was previously adjusted (from WARNING) on an earlier version of v4 because of the usage of custom logging. Now that that's effectively removed as of ~#421, the log.info() prints out to regular console terminals
(which then is treated as a fancy print() statement), and moreover, this statement does not primarily concern bot devs, hence the change.

Checklist

• I've ran pre-commit to format and lint the change(s) made.
• I've checked to make sure the change(s) work on 3.8.6 and higher.
• This fixes/solves an Issue.
  • (If existent):
• I've made this pull request for/as: (check all that apply)
  • [] Documentation
  • Breaking change
  • New feature/enhancement
  • Bugfix