The GITHUB_WORKSPACE is set with an incorrect directory

[BrightRan]

Associated GitHub Community ticket: https://github.community/t/github-actions-is-setting-github-workspace-incorrectly/132187

The customer has a workflow like as below:

name: CI
env:
  JAVA_VERSION: 11.0.7
  NOW: $(($(date +%s%N)/1000000))
on:
  pull_request:
jobs:
  evaluate-environment:
    name: Look at the environment
    runs-on: [self-hosted, humio, special]
    steps:
      - name: Print github workspace
        run: |
          echo "GITHUB_WORKSPACE = $GITHUB_WORKSPACE"
          echo "github.workspace = ${{ github.workspace }}"
          echo "pr.ref = ${{github.event.pull_request.head.ref}}"
          echo "github.ref = ${{ github.ref }}"
          echo "$GITHUB_CONTEXT"
        env:
          GITHUB_CONTEXT: ${{ toJson(github) }}

  checkout-code:
    name: Check out the code and see what ref comes out
    runs-on: [self-hosted, humio, special]
    steps:
      - name: Remove existing git hooks
        run: git config --unset core.hooksPath && rm -rf .git/hooks/ || true

      - uses: actions/checkout@v2
        with:
          path: ${{ github.ref }}
          clean: true
          lfs: true

      - name: Checkout LFS
        run: git lfs checkout

      - name: Print workspace path
        run: echo $GITHUB_WORKSPACE && pwd && echo ${{github.ref}}

      - name: current checkout
        run: git log -10

When viewing the value of 'GITHUB_WORKSPACE' and 'github.workspace' printed in the logs, he found that the path was "/actions-runner/gh-ci-01/_work/humio/refs/pull/8401/merge".
Normally, the path of the default workspace should like as below:

<runner-installation-directory>/_work/<repo-name>/<repo-name>
OR
<runner-installation-directory>/work/<repo-name>/<repo-name>

In the customer's case, the correct path should be "/actions-runner/gh-ci-01/_work/humio/humio". But why the path was changed?

[BrightRan]

According to what has been mentioned in "actions/runner#702", it seems that the checkout action can change the path of the default workspace and cause error like "No such file or directory".
Is this problem also related to the issue of the checkout action?

[srdo]

Just to make sure this is not missed: The path /actions-runner/gh-ci-01/_work/humio/refs/pull/8401/merge is mentioning pull request 8401, but the action is running as part of the workflow for pull request 8410. This seems wrong.