Build(GHActions): Use checkout@v4 instead of outdated v2

.github/workflows/test-publish.yaml

@@ -34,7 +34,7 @@ jobs:
     steps:
 
       # Setup Python/pip
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: s-weigand/setup-conda@v1
         with:
           conda-channels: conda-forge