chore: Add setup-dependencies directory to Dependabot config (#133)

# Pull Request

## Description

This change updates the Dependabot configuration to monitor GitHub
Actions dependencies in an additional directory. Specifically, it adds
the ".github/actions/setup-dependencies" directory to the list of
monitored paths. This ensures that Dependabot will check for updates in
both the root directory and the setup-dependencies action directory,
potentially improving the maintenance and security of the project's
GitHub Actions.

fixes #134

.github/dependabot.yml

@@ -2,7 +2,9 @@ version: 2
 
 updates:
   - package-ecosystem: "github-actions"
-    directory: "/"
+    directories:
+      - "/"
+      - ".github/actions/setup-dependencies"
     commit-message:
       prefix: "deps(github-actions)"
     schedule: