This change should prevent old clients (e.g., Android 6) from
failing to perform a ndt7 experiment because their internal CA
bundle is now too old.
Reference issue: https://github.com/ooni/probe/issues/2031
While there, run `go mod tidy` to fix a minor inconsistence in
the current `go.mod` file.
This diff WILL require a backport to release/3.14.