The Windows Server 2016 virtual environment will be removed on November 7, 2019. You will need to update your workflow files to run on windows-latest which will run on the Windows Server 2019 environment instead.
actions/runner-images#68
We use windows-2016:
actions/runner-images#68
We use
windows-2016:Pillow/.github/workflows/test-windows.yml
Line 8 in 64e1fee