github actions: reorder things
github actions: reorder things

I realized the go.mod/go.sum file is modified when running 'go get' from
a checkout.

So fetch the tools *before* checking out. Now, we can run go generate
check safely last.

Still need to figure out how to run the go generate check on Windows.

Change the cache key to not use the go.sum, since it's irrelevant, we
want to cache the tools.

periph/bootstrap,periph/bootstrap