Go artifact caching will help provided that the cache remains small
enough - we can reuse the strategy from the Windows build where we only
cache and pull the zips, but let go(1) do the many-file unpacking as it
does so faster.
The race matrix was building once without race, then running all the
tests with race, so change the matrix to incldue a `buildflags`
parameter and use that both in the build and test steps.
Updates #cleanup
Signed-off-by: James Tucker <james@tailscale.com>
James Tucker
b7f51a1468