Resolve "In GraphGroup, improve warning on changed graph size"

This MR improves the GraphGroups warnings on changed graph size when adding property data to a graph.

Anything to double-check?

Can this MR be accepted?

• Implementation ready
• Tests added or adjusted
• Documentation extended or updated

• Code quality
  • Changes follow coding guidelines
  • Checked code coverage on new and adjusted code

• Ready for merging
  • Pipeline passes without warnings
  • History cleaned-up or squash option set
  • Changelog entry added
  • Version number bumped to v1.0.0a0
  • Reviewed & approved by @

Related issues

Closes #232 (closed)