fix(frontend): display bug on add knowledge (#2644)

# 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):

frontend/lib/components/UploadDocumentModal/UploadDocumentModal.module.scss

@@ -9,6 +9,7 @@
   background-color: var(--background-0);
   width: 100%;
   flex: 1;
+  overflow: hidden;
 
   .buttons {
     display: flex;