CI: github: use the GITHUB_TOKEN instead of a manually generated token

Github allows to use a auto generated GITHUB_TOKEN so we don't need to
handle the token in the secret configuration.

https://docs.github.com/en/actions/security-guides/automatic-token-authentication#about-the-github_token-secret

.github/workflows/vtest.yml

@@ -25,6 +25,8 @@ jobs:
     steps:
       - uses: actions/checkout@v3
       - name: Generate Build Matrix
+        env:
+          GITHUB_API_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         id: set-matrix
         run: python3 .github/matrix.py "${{ github.ref_name }}"