Add dependabot to keep github-actions up-to-date

Signed-off-by: yubiuser <github@yubiuser.dev>

.github/dependabot.yml

@@ -0,0 +1,10 @@
+version: 2
+updates:
+- package-ecosystem: github-actions
+  directory: "/"
+  schedule:
+    interval: weekly
+    day: saturday
+    time: "10:00"
+  open-pull-requests-limit: 10
+  target-branch: master