Syntax highlighting is broken on file extensions that don't match case

Created by: RichardBelzer

• Sourcegraph version: 3.18.0
• Platform information: Fedora Server

Steps to reproduce:

Have a file in the repo that is all caps

Expected behavior:

The syntax highlighting works:

Actual behavior:

Everything is all grey. It doesn't think it's a source file.

This is probably a case where .lower() is not being called on the filename to match against supported source file types