Use Dependabot to update GitHub actions

Author: grubersjoe

.github/dependabot.yml

@@ -12,7 +12,7 @@ updates:
         update-types:
           - 'minor'
           - 'patch'
-  - package-ecosystem: 'docker'
+  - package-ecosystem: 'github-actions'
     directory: '/'
     schedule:
       interval: 'weekly'