* Packer plugins rely on the Packer SDK for the majority of its HCL
dependency. To prevent issues with the version of go-cty or hcl/v2 pkg
getting out of sync this changes sets the allowed dependency to
packer-plugin-sdk only.
* HashiCorp is standardizing on pinning versions of allowed GitHub actions to prevent
the introduction of potential security issues. This change removes GitHub actions
from dependabot.