Chore: remove unused environment variables from `ci.yml`

[nelsonic]

At present we have a few unused environment/action variables in the ci.yml file: https://github.com/dwyl/mvp/blob/1f87fa6dfdf0bc9d49ca0eca50520a7fa1e8b7c6/.github/workflows/ci.yml#L42-L52

These are the 3 we actually need: https://github.com/dwyl/mvp/settings/secrets/actions

Todo

• [ ] Remove the unused environment variables so they aren't confusing to a new person on the team.

[nelsonic]

PR: #138 ✅