GHA: use actions/checkout@v2 everywhere

Author: junghans

.github/workflows/copyright.yml

@@ -27,7 +27,7 @@ jobs:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
       - name: Checkout head branch from PR
         if: ${{ fromJSON(steps.issue_info.outputs.data).pull_request }}
-        uses: actions/checkout@v2.2.0
+        uses: actions/checkout@v2
         with:
           repository: ${{ fromJSON(steps.pr_info.outputs.data).head.repo.full_name }}
           ref: ${{ fromJSON(steps.pr_info.outputs.data).head.ref }}

.github/workflows/create-pr.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@master
+        uses: actions/checkout@v2
         with:
           ref: ${{ github.event.ref }}
           fetch-depth: 0