This works on my side:

steps:
  - checkout: self
    persistCredentials: true

  # Rest of the pipeline

  - script: |
      git config --global user.name "BuildService"
      git config --global user.email "[email protected]"
      git tag "Build_$(Build.BuildNumber)"
      git push origin --tags
    workingDirectory: '$(Build.Repository.LocalPath)'

Running Git commands inside Azure DevOps pipeline