add dependabot.yml (#218)

Author: bsadashi

.github/dependabot.yml

@@ -0,0 +1,16 @@
+---
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      updates:
+        applies-to: version-updates
+        patterns:
+          - "*"
+      security-updates:
+        applies-to: security-updates
+        patterns:
+          - "*"