chore: add github-actions ecosystem to dependabot coverage (#7)

This repo lacked dependabot coverage for the github-actions ecosystem,
which is how the Node 20 deprecation accumulated silently before
DTD#18 surfaced it as a deadline-driven scramble.

Adds .github/dependabot.yml with weekly github-actions update checks.
Future deprecations will surface as PRs rather than needing manual
ecosystem audits.

Refs TMHSDigital/Developer-Tools-Directory#31.

Signed-off-by: 154358121+TMHSDigital@users.noreply.github.com
Made-with: Cursor

Signed-off-by: 154358121+TMHSDigital@users.noreply.github.com

Author: TMHSDigital

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"