ci: add Dependabot for GitHub Actions

.github/dependabot.yml

diff --git a/.github/dependabot.yml b/.github/dependabot.yml
new file mode 100644
index 0000000..c78a085
--- /dev/null
+++ b/.github/dependabot.yml
@@ -0,0 +1,7 @@
+version: 2
+updates:
+  # GitHub Actions
+  - package-ecosystem: github-actions
+    directory: /
+    schedule:
+      interval: daily