Update actions/checkout action to v4

Author: renovate[bot]

.github/workflows/docker.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Cache pipenv virtualenvs incl. all pip packages
       uses: actions/cache@v2

.github/workflows/vagrant.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: macos-10.15
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v4
 
     - name: Cache pipenv virtualenvs incl. all pip packages
       uses: actions/cache@v2