chore: improve no iterations found feedback

ucam_gitlab_stats/cli.py

@@ -115,6 +115,10 @@ def mean_capacity(
         print(
             f"Mean iteration capacity last {week_count} weeks: {capacity_sum/capacity_count}"
         )
+    else:
+        print(
+            f"No iterations found."
+        )
 
 
 if __name__ == "__main__":