DEV: Upgrade actions/cache to v2 (PR #10920)

https://github.com/actions/cache/issues/381#issuecomment-662597653

v1 has issues with slow cache restoration. Tested with v2 in a branch on knowledge-explorer and it seemed to fire up quite a bit faster.

GitHub

Awesome, if that’s easy!

We need to merge this ASAP, it hangs for 30 minutes sometimes

We need to merge this ASAP, it hangs for 30 minutes sometimes

GH Actions has been flaky the last couple of weeks, too. Actions randomly cancelled or failing to complete. Hopefully this will help!