Error: The process '/usr/bin/git' failed with exit code 128

Couple of days back this action stopped working.

    - name: Checkout private tools
      uses: actions/checkout@v2
      with:
        repository: tectonic/infrastructure-helm
        token: ${{ secrets.GIT_TECHDEPLOY_TOKEN }}
        path: infrastructure-helm
        fetch-depth: 0
        ref: master

Run actions/checkout@v2
/usr/bin/docker exec  d0faea3798ca7561c881e147e6613d25f75372e481a2c181696cc87de585d470 sh -c "cat /etc/*release | grep ^ID"
Syncing repository: tectonic/infrastructure-helm
Getting Git version info
Initializing the repository
Disabling automatic garbage collection
Setting up auth
Fetching the repository
  /usr/bin/git -c protocol.version=2 fetch --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/tags/*:refs/tags/*
  remote: Repository not found.
  Error: fatal: repository 'https://github.com/tectonic/infrastructure-helm/' not found
  The process '/usr/bin/git' failed with exit code 128
  Waiting 19 seconds before trying again
  /usr/bin/git -c protocol.version=2 fetch --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/tags/*:refs/tags/*
  remote: Repository not found.
  Error: fatal: repository 'https://github.com/tectonic/infrastructure-helm/' not found
  The process '/usr/bin/git' failed with exit code 128
  Waiting 11 seconds before trying again
  /usr/bin/git -c protocol.version=2 fetch --prune --progress --no-recurse-submodules origin +refs/heads/*:refs/remotes/origin/* +refs/tags/*:refs/tags/*
  remote: Repository not found.
  Error: fatal: repository 'https://github.com/tectonic/infrastructure-helm/' not found
  Error: The process '/usr/bin/git' failed with exit code 128

Seems similar to this issue: https://github.com/ad-m/github-push-action/issues/76

Start with the actions/checkout@v2 workflow step and its failing git fetch log for the private repository. Trace how the repository and GIT_TECHDEPLOY_TOKEN are configured, then use the reported checkout run to reproduce the failure. Done means the workflow can fetch the private repository successfully without exit code 128.