Wrong Content-Type for Documents and Attachments

Summary

Microsoft Office XML Documents (and maybe more?) are sent with MIME zip instead of the correct MIME-Type.

Steps to reproduce

Try to download any .docx, .xlsx, .pptx from a repo or the wiki.

Example Project

https://gitlab.com/the_s/OfficeXmlDownload

What is the current bug behavior?

The document is sent to the browser as "zip", so it cannot be opened with Word/Excel/Powerpoint.

What is the expected correct behavior?

The document ist sent with the correct MIME-Type, so the browser offers to open it with Word/Excel/Powerpoint.

Results of GitLab environment info

Happens on GitLab.com.