Set package-mode to false in poetry config

[mjgiarlo]

I found that poetry install was returning this locally:

$ poetry install
The "poetry.dev-dependencies" section is deprecated and will be removed in a future version. Use "poetry.group.dev.dependencies" instead.
Installing dependencies from lock file

No dependencies to install or update

Installing the current project: was_robot_suite (0.1.0)
Warning: The current project could not be installed: No file/folder found for package was-robot-suite
If you do not want to install the current project use --no-root.
If you want to use Poetry only for dependency management but not for packaging, you can disable package mode by setting package-mode = false in your pyproject.toml file.
If you did intend to install the current project, you may need to set `packages` in your pyproject.toml file.

Patching this change in got me past the error. We do this already in was-pywb. I assume it's appropriate here? cc: @lwrubel @edsu