Investigate if we can share resources between github actions jobs

[kenzieschmoll]

Right now, every job pays the cost of cloning the flutter repo and building flutter tools (right now twice - see https://github.com/flutter/devtools/issues/4591). This is part of the bots.sh script. We should investigate if there is a way to perform this action in a setup step so that we only have to pay this cost once, not for every job.