Dependabot checks GitHub Actions files

The code was copied from the example at
https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#directory.

Author: ddabble

.github/dependabot.yml

@@ -5,3 +5,9 @@ updates:
     directory: "/requirements"
     schedule:
       interval: "daily"
+
+  - package-ecosystem: "github-actions"
+    # Workflow files stored in the default location of `.github/workflows`
+    directory: "/"
+    schedule:
+      interval: "weekly"