Add Dependabot configuration for GitHub Actions updates (#9)

## Description

This pull request introduces a Dependabot configuration file to automate
dependency updates for GitHub Actions in the repository. This helps
ensure that GitHub Actions workflows remain up-to-date with the latest
security and feature updates.

Dependency management automation:

* Added a `.github/dependabot.yml` file to enable weekly automated
updates for GitHub Actions dependencies, with appropriate labels for
tracking.

Author: MariusStorhaug

.github/dependabot.yml

@@ -0,0 +1,14 @@
+# To get started with Dependabot version updates, you'll need to specify which
+# package ecosystems to update and where the package manifests are located.
+# Please see the documentation for all configuration options:
+# https://docs.github.com/github/administering-a-repository/configuration-options-for-dependency-updates
+
+version: 2
+updates:
+  - package-ecosystem: github-actions # See documentation for possible values
+    directory: / # Location of package manifests
+    labels:
+      - dependencies
+      - github-actions
+    schedule:
+      interval: weekly