Dropping an image on a commit comment doesn't attach the file

Issue Summary

Unable to drag and drop an image file onto a commit comment (the same functionality works fine for PR comments).

This is reproducible on Data Center: yes

Steps to Reproduce

(I performed the below steps in Chrome)

1. Open a commit diff
2. Add a comment somewhere on a file
3. Drag an image over the comment to attach the image to the file

Expected Results

A drop target appears and the file is attached to the comment

Actual Results

No drop target appears and, instead, Chrome opens the image in a new tab.

Workaround

Users need to use the "Attach file" button to add an image to the comment.