fix: enable Windows long path support in GitHub Actions

[thomhurst]

Summary

Fixes PathTooLongException errors on Windows CI by enabling long path support (>260 characters) via registry setting.

Problem

Windows CI was failing with:

System.IO.PathTooLongException: The specified path, file name, or both are too long. The fully qualified file name must be less than 260 characters, and the directory name must be less than 248 characters.

This occurred during source generation for test methods with complex generic signatures like GenericMethodTests.AggregateBy_HasExpectedOutput<TSource, TKey, TAccumulate>(...).

Solution

Enable Windows long path support in GitHub Actions by setting the LongPathsEnabled registry key before building. This is a cleaner solution than modifying source generator code to hash long filenames.

Test Plan

• Windows CI should pass without PathTooLongException
• Source generator tests with long method names should work

Fixes: https://github.com/thomhurst/TUnit/actions/runs/21610514651

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

This is a clean solution to the Windows long path issue. Enabling long path support at the system level is the right approach rather than working around it in the source generator.

[Frulfump]

Will this force users to also use long paths to avoid potential issues? Could your CI now hide issues that users would run into otherwise?