Can we use GHA caching of the checked-out code and dependencies to reduce build burden?

Analyzing the dynamic_bitset gcc-9 build job, the "Setup Boost" took 1m 8s while "Run tests" took 30s. If we're paying 1m 8s on every job, we could probably do that part once and then cache the result, and same a bunch of time leveraging GHA's caching mechanism.