Update dart_skills_lint dependency to e449787 and centralize test configuration

[reidbaker]

Updates the pinned dart_skills_lint reference in tool/pubspec.yaml to commit hash e4497873950727ee781fa411c1a2f624b1ec50c6 (version 0.3.0). Refactors tool/test/validate_skills_test.dart to load configuration dynamically via ConfigParser.loadConfig and omit targeting overrides, enabling native path inheritance from tool/dart_skills_lint.yaml.

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[gemini-code-assist]

Code Review

This pull request updates the dart_skills_lint dependency to version 0.3.0 and refactors the validate_skills_test.dart to use a configuration file (dart_skills_lint.yaml) via ConfigParser instead of hardcoded values. This change fulfills a previous TODO and streamlines the skill validation process. I have no feedback to provide.