Generator tests are failing on master

After updating Golang to 1.17, generator packaging tests started to fail with the following error:
```
../../../pkg/mod/github.com/elastic/beats/v7@v7.0.0-alpha2.0.20211012102339-11c72774f8b6/dev-tools/packaging/package_test.go:39:2: missing go.sum entry for module providing package github.com/blakesmith/ar; to add:
        go mod download github.com/blakesmith/ar

```