Expand error message from providers with rel_file_pattern used?

[anders-kiaer]

E.g. here

webviz-subsurface/webviz_subsurface/_providers/ensemble_summary_provider/ensemble_summary_provider_factory.py

Lines 221 to 224 in 0670839

	if not per_real_tables:
	raise ValueError(
	f"Could not find any .arrow unsmry files for ens_path={ens_path}"
	)

.