Video preview not working

Summary

I attached an MP4 file to a comment on a MR, and it shows up like:

Steps to reproduce

(How one can reproduce the issue - this is very important)

Example Project

(If possible, please create an example project here on GitLab.com that exhibits the problematic behavior, and link to it here in the bug report)

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What is the current bug behavior?

The HTML for it is:

<a class="no-attachment-icon" href="https://gitlab.com/<redacted>/ScreenRecording_06-06-2019_12-14-17.MP4" target="_blank" rel="noopener noreferrer">
    <img src="https://gitlab.com/<redacted>/ScreenRecording_06-06-2019_12-14-17.MP4" alt="ScreenRecording_06-06-2019_12-14-17" class="js-lazy-loaded qa-js-lazy-loaded">
</a>

What is the expected correct behavior?

The src of the img tag should not be pointing to a video, I think.

Output of checks

This bug happens on GitLab.com