The deploy_unmanaged flow is supposed to silently do nothing if there's not actually a package directory

[prescod]

The deploy_unmanaged flow is supposed to silently do nothing if there's not actually a package directory

Originally posted by @davisagli in https://github.com/SFDO-Tooling/CumulusCI/pull/2783#discussion_r690774539

 $  cci org scratch_delete qa && cci flow run qa_org --org qa

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2021-08-24 17:32:18: ------------------------------------------------------------
2021-08-24 17:32:18: Running task: update_package_xml
2021-08-24 17:32:18: ------------------------------------------------------------
2021-08-24 17:32:18: 
2021-08-24 17:32:18: Options:
2021-08-24 17:32:18:   path: src
2021-08-24 17:32:18:   managed: False
2021-08-24 17:32:18: Beginning task: UpdatePackageXml
2021-08-24 17:32:18: 
2021-08-24 17:32:18: Generating src/package.xml from metadata in src
2021-08-24 17:32:18: Exception in task deploy_unmanaged.update_package_xml