raise dependencyFile not resolvable error for incompatible version constraints

[a-schur]

What are you trying to accomplish?

I am improving error handling in the Python ecosystem for Dependabot by raising a DependencyFileNotResolvable error when Poetry encounters incompatible version constraints. This is to ensure that these specific errors are surfaced clearly to users and can be debugged more easily.

Anything you want to highlight for special attention from reviewers?

• There are still additional Sentry events with the same Dependabot::SharedHelpers::HelperSubprocessFailed: Creating virtualenv ... error, but with different error messages after that.
• The current PR only matches errors containing "Cannot enrich dependency with incompatible constraints:".
• I plan to add more regex patterns and test cases to catch other similar errors that do not include this phrase, as seen in related Sentry sub-events.
• Please review the regex and error handling logic for completeness and maintainability.

How will you know you've accomplished your goal?

• The specific Sentry errors with "Cannot enrich dependency with incompatible constraints:" are now caught and reported as DependencyFileNotResolvable.
• Additional test cases will be added to ensure these errors are handled and surfaced correctly.
• I will monitor Sentry to confirm that these errors are no longer unhandled, and will iterate to catch other related error patterns as needed.

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

[thavaahariharangit]

LGTM