fix upload file error in online mode

src/workflow/StreamlitUI.py

@@ -70,6 +70,9 @@ def upload_widget(
                 if files:
                     files_dir.mkdir(parents=True, exist_ok=True)
                     for f in files:
+                        # in case of online mode a single file is returned -> put in list
+                        if not isinstance(files, list):
+                            files = [files]
                         if f.name not in [
                             f.name for f in files_dir.iterdir()
                         ] and f.name.endswith(file_type):
@@ -687,4 +690,4 @@ def execution_section(self, start_workflow_function) -> None:
                     st.code(f.read(), language="neon", line_numbers=True)
 
     def results_section(self, custom_results_function) -> None:
-        custom_results_function()
+        custom_results_function()