fix: Fix error message in SummaryAssistant class (#2453)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

backend/modules/assistant/ito/summary.py

@@ -50,7 +50,7 @@ class SummaryAssistant(ITO):
         if len(self.files) > 1:
             raise ValueError("Only one file can be uploaded")
         if not self.input.inputs.files:
-            raise ValueError("No files were given in the input")
+            raise ValueError("No files key were given in the input")
         if len(self.input.inputs.files) > 1:
             raise ValueError("Only one file can be uploaded")
         if not self.input.inputs.files[0].key == "doc_to_summarize":