chore: fix flake str issue

Signed-off-by: David Wallace <mypydavid@proton.me>

Author: David Wallace

src/raman_fitting/delegators/run_fit_spectrum.py

@@ -38,11 +38,9 @@ def run_fit_over_selected_models(
     prepared_spectra = prepare_aggregated_spectrum_from_files(raman_files)
 
     if not prepared_spectra:
-        errors = "\n".join(
-            map(str, processing_errors.get_errors_for_files(raman_files))
-        )
+        errors = ",".join(map(str, processing_errors.get_errors_for_files(raman_files)))
 
-        logger.error("These files do not contain any valid data.\n" f"{errors}")
+        logger.error(f"These files do not contain any valid data: {errors}")
         return None
 
     for region, models_for_region in models.items():