Git Trees API returns 404 instead of 403 when workflow scope is missing for .github/workflows/* files

[sthobis]

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Bug

Body

When using the Git Data API's Create a tree endpoint (POST/repos/{owner}/{repo}/git/trees) with a classic OAuth token that has repo scope but not workflow scope, and the tree includes entries under .github/workflows/, the API returns 404 Not Found instead of 403 Forbidden.

This is extremely misleading and difficult to debug because:

• The 404 response gives no indication that the issue is a missing scope
• Other Git Data API endpoints (blobs, refs, commits) work fine with the same token on the same repo
• The X-Accepted-OAuth-Scopes header on the 404 response is empty, providing no hint about the required workflow
  scope

Steps to reproduce

1. Create a classic OAuth App
2. Authorize with scope=repo (no workflow scope)
3. Create a repo via POST /user/repos with auto_init: true
4. Create blobs via POST /repos/{owner}/{repo}/git/blobs — succeeds
5. Create a tree via POST /repos/{owner}/{repo}/git/trees with an entry whose path is
   .github/workflows/deploy.yml — returns 404

Request

POST /repos/{owner}/{repo}/git/trees
Authorization: Bearer <token with repo scope only>
Accept: application/vnd.github+json
Content-Type: application/json

{
  "tree": [
    {
      "path": ".github/workflows/deploy.yml",
      "mode": "100644",
      "type": "blob",
      "sha": "<valid blob sha>"
    }
  ]
}

Response

HTTP 404
X-OAuth-Scopes: repo
X-Accepted-OAuth-Scopes:

{
  "message": "Not Found",
  "documentation_url": "https://docs.github.com/rest/git/trees#create-a-tree",
  "status": "404"
}

Expected behavior

The API should return 403 Forbidden with a message indicating that the workflow scope is required to create or modify files under .github/workflows/. Ideally, the X-Accepted-OAuth-Scopes header should include workflow.

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