Curations use `commit` instead of `tree` for GitHub source urls

Harvested data shows uses `tree` for GitHub source location, but when you submit a curation to edit the source location, it changes to `commit`. According to this PR, it looks like the website uses the Harvest UI picker, which uses `commit`. Everything else I could fine uses `tree`.
https://github.com/clearlydefined/website/pull/344/commits/6d1bc7da18dbc861036cd44dcb8c387f4434b33b

- Harvested source location:
- https://clearlydefined.io/definitions/git/github/mono/mono/abad3612068e7333956106e7be02d9ce9e346f92
- Curated source location:
- https://clearlydefined.io/definitions/sourcearchive/mavencentral/org.apache.httpcomponents/httpcore-nio/4.4.15/4.4.15