disambiguate direct-origin dependencies in show-outdated

[dimbleby]

if you have, say:

[tool.poetry.dependencies]
poetry = "^1.2.0b3"

[tool.poetry.dev-dependencies]
poetry = {git = "https://github.com/python-poetry/poetry.git"}

and go poetry show --outdated then you hit the runtime error Unknown direct dependency type None.

The reason is that poetry appears twice, once as a direct dependency and once not. And we happen to search for the direct dependency using the one that isn't, if you see what I mean.

This MR also improves the error message by saying which package is the problematic one.

[mkniewallner]

Since we have a way to reproduce the problem, should we add a non-regression test?

[dimbleby]

sure, go for it

[github-actions]

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