dependabot: Enable for GitHub Actions (#377)

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
index eed0ba6..405de40 100644
--- a/.github/dependabot.yml
+++ b/.github/dependabot.yml
@@ -5,3 +5,9 @@
     schedule:
       interval: "daily"
     labels: ["dependencies"]
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    labels: ["dependencies"]