Enable Dependabot ignore directives

This enables the Dependabot ignore directives for GitHub Actions.

.github/dependabot.yml

@@ -11,10 +11,10 @@ updates:
     directory: "/"
     schedule:
       interval: "weekly"
-    # ignore:
+    ignore:
-    #   - dependency-name: actions/cache
+      - dependency-name: actions/cache
-    #   - dependency-name: actions/checkout
+      - dependency-name: actions/checkout
-    #   - dependency-name: actions/setup-python
+      - dependency-name: actions/setup-python
 
   - package-ecosystem: "pip"
     directory: "/"