Add dependabot config for grouped GitHub Actions updates

Agent-Logs-Url: https://github.com/cryptomator/cryptomator.github.io/sessions/d6e7857c-a424-49fb-9845-d5dd5f6b43bc

Co-authored-by: infeo <9036915+infeo@users.noreply.github.com>

Author: Copilot

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+    groups:
+      github-actions:
+        patterns:
+          - "*"