[eas-cli] Fix workflow detection for tracked gitignored files

[sjchmiela]

Why

resolveWorkflowAsync() decides between managed and generic by checking whether native workflow markers exist and whether vcsClient.isFileIgnoredAsync() says they are ignored.

After the recent Git client rework, GitClient.isFileIgnoredAsync() treated tracked files as never ignored when there was no .easignore. That matches a checked-out clone when requireCommit: true, but it does not match the requireCommit: false archive path, where we create a repo with --no-checkout and then copy the working tree with .gitignore filtering.

That mismatch can make workflow detection report GENERIC even though the uploaded archive no longer contains the native project.

How

• use git check-ignore --no-index when requireCommit is false, so tracked files that would be filtered out of the working tree copy are treated as ignored
• keep the existing tracked-file behavior when requireCommit is true, because those builds rely on a Git checkout
• extend the Git client tests to cover tracked .gitignore matches
• add a Git-backed workflow regression test that exercises resolveWorkflowAsync() directly

Test Plan

• Added integration-style tests for GitClient.isFileIgnoredAsync() behavior with tracked .gitignore matches
• Added a Git-backed resolveWorkflowAsync() regression test for the requireCommit: false vs requireCommit: true split
• I could not run the test suite locally in this environment because yarn is not installed

[github-actions]

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File Patterns	Mentions
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[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 54.38%. Comparing base (3945763) to head (7e912ca).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3561      +/-   ##
==========================================
+ Coverage   54.38%   54.38%   +0.01%     
==========================================
  Files         824      824              
  Lines       35420    35421       +1     
  Branches     7318     7319       +1     
==========================================
+ Hits        19258    19259       +1     
  Misses      16075    16075              
  Partials       87       87              

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