Bump to actions/checkout@v4

actions/checkout@v3 uses nodejs 16 that is deprecated

Author: stronk7

.github/workflows/test_buildx_and_publish.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Build image
         run: |
@@ -43,7 +43,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       # Calculate the tags to be pussed to the registries.
       - name: Calculate image tag names