has_persistent_tasks: use add not dev

[asinghvi17]

In situations where the targeted package has a sources section this will try to dev the package. Pkg then tries to find the packages indicated in sources, which will all be local paths assuming a monorepo structure, except those don't exist - because this is the stripped tarball you get from a Pkg server and not the full repo structure.

Using add should "just fix" that.