Description
Per the documentation: https://docs.github.com/en/free-pro-team@latest/actions/reference/environment-variables#default-environment-variables
The GITHUB_WORKSPACE variable should evaluate to a path. When using in a workflow (after checkout) however, it is evaluating to nothing and not providing the path both on ubuntu-latest/windows-latest

Example: https://github.com/timheuer/buildtest/runs/1243185809?check_suite_focus=true#step:3:2 from workflow: https://github.com/timheuer/buildtest/blob/master/.github/workflows/build.yml#L40

Area for Triage:
Servers

Question, Bug, or Feature?:
Bug

Virtual environments affected

• macOS 10.15
• Ubuntu 16.04 LTS
• Ubuntu 18.04 LTS
• Ubuntu 20.04 LTS
• Windows Server 2016 R2
• Windows Server 2019

Expected behavior
I expect to see a full path to the workspace per documentation

Actual behavior
A blank variable is provided

Repro steps
See example repo that has an echo of the variable evaluating to nothing