Use Dependabot to update local composite actions

The 'directory: /' configuration only looks at workflows.

Author: cbandy

.github/dependabot.yml

@@ -2,12 +2,14 @@
 # https://docs.github.com/code-security/dependabot/dependabot-version-updates/customizing-dependency-updates
 #
 # See: https://www.github.com/dependabot/dependabot-core/issues/4605
----
 # yaml-language-server: $schema=https://json.schemastore.org/dependabot-2.0.json
+---
 version: 2
 updates:
   - package-ecosystem: github-actions
-    directory: /
+    directories:
+      - '/'
+      - '.github/actions/*'
     schedule:
       interval: weekly
       day: tuesday