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src/incremental/newsfragments/106.bugfix

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+Incremental could mis-identify that a project had opted in to version management.
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+If a ``pyproject.toml`` in the current directory contained a ``[project]`` table with a ``name`` key, but did not contain the opt-in ``[tool.incremental]`` table, Incremental would still treat the file as if the opt-in were present and attempt to validate the configuration. This could happen in contexts outside of packaging, such as when creating a virtualenv. When operating as a setuptools plugin Incremental now always requires the ``[tool.incremental]`` opt-in.  Additionally, it suppresses any exceptions that occur while attempting to read ``pyproject.toml`` until it finds a valid ``[tool.incremental]`` table.