Github submodule links don't resolve correctly

Created by: muratsu

• Sourcegraph version: 3.29
• Platform information: dotcom

Steps to reproduce:

1. Navigate to the repo (https://sourcegraph.com/github.com/Irev-Dev/cadhub/-/tree/app/web/src)
2. Click on the cascade repo link

Expected behavior:

1. Cascade link to point to https://github.com/Irev-Dev/CascadeStudio/tree/cd23a8e67358278e96ec37505cf0fcc616e93225

Actual behavior:

1. Cascade link points to sourcegraph.com