add GHA support to dependabot (#5544)

* add GHA support to dependabot

* add labels

* Update .github/dependabot.yml

Co-authored-by: Chevdor <chevdor@users.noreply.github.com>

Co-authored-by: Chevdor <chevdor@users.noreply.github.com>

polkadot/.github/dependabot.yml

@@ -19,3 +19,8 @@ updates:
       - dependency-name: "sub-tokens"
     schedule:
       interval: "daily"
+  - package-ecosystem: github-actions
+    directory: '/'
+    labels: ["A2-insubstantial", "B0-silent", "C1-low 📌", "E3-dependencies"]
+    schedule:
+      interval: daily