Freeze checkout action version

Fixes #24 
Fixes #25 
Fixes #26

Author: fkorotkov

README.md

@@ -23,7 +23,7 @@ jobs:
     steps:
     - uses: actions/checkout@master
     - name: Automatic Rebase
-      uses: cirrus-actions/rebase@master
+      uses: cirrus-actions/rebase@v1.2.0
       env:
         GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
   # https://github.community/t5/GitHub-Actions/Workflow-is-failing-if-no-job-can-be-ran-due-to-condition/m-p/38186#M3250