Duplicate Content-Length Headers

[kendrome]

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Describe the bug

The webserver duplicates the Content-Length header when accessing static files, like CSS, JS, and JSON files. This causes issues with some web clients like aiohttp. This exists on 0.6.3 and 0.7.0-rc12

To Reproduce

Inspect any request of a static file, examples style.css and main.js

Expected behavior

There should only be a single header for Content-Length

Screenshots or video