The CI should be set up to retain the Go module and build caches, so
we'll avoid downloading it multiple times. This avoids having to
replicate some code.
Update-Note: The tests now have a golang.org/x/crypto dependency. This
should be fetched transparently with Go modules. Monorepos with
different import path conventions may need to rewrite these imports.
Change-Id: If5ba52e051f180536d72109c2e690bbd13d58e7c
Reviewed-on: https://boringssl-review.googlesource.com/c/boringssl/+/42044
Reviewed-by: Adam Langley <agl@google.com>
Commit-Queue: David Benjamin <davidben@google.com>