Enable dependabot ignore directives

Enable all of the dependabot ignore directives managed by the
cisagov/skeleton-python-library project.

Author: mcdonnnj

.github/dependabot.yml

@@ -19,9 +19,9 @@ updates:
       - dependency-name: actions/setup-python
       - dependency-name: hashicorp/setup-terraform
       - dependency-name: mxschmitt/action-tmate
-      # # Managed by cisagov/skeleton-python-library
-      # - dependency-name: actions/download-artifact
-      # - dependency-name: actions/upload-artifact
+      # Managed by cisagov/skeleton-python-library
+      - dependency-name: actions/download-artifact
+      - dependency-name: actions/upload-artifact
 
   - package-ecosystem: "pip"
     directory: "/"