Is there an existing issue for this?

• I have searched the existing issues

Package ecosystem

pip

Package manager version

No response

Language version

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Manifest location and content before the Dependabot update

No response

dependabot.yml content

version: 2
updates:

• package-ecosystem: "pip"
  directory: "/"
  schedule:
  interval: "daily"

Updated dependency

No response

What you expected to see, versus what you actually saw

Expected: dev dependencies are read from requirements-dev.txt from the same repo.
Actual: dependency_file_not_parseable

Native package manager behavior

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Images of the diff or a link to the PR, issue, or logs

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Smallest manifest that reproduces the issue

pyproject.toml with

[tool.setuptools]
dynamic.optional-dependencies = {dev = { file = ["requirements-dev.txt"] }}

and any requirement-dev.txt in the classic format