Update CI to run on main branch and run some jobs nightly
This PR makes two small changes to the Github Actions CI
- run all jobs on the
main
branch - this just means that if we renamemaster
tomain
we don't have to update the CI again - run the
Dependencies
workflow on a cron schedule every night - this should allow us to catch breaking changes in dependencies as early as possible, rather than 'whenever the next person submits a PR'