Add dependabot on Github actions

.github/dependabot.yml

@@ -0,0 +1,10 @@
+# Set update schedule for GitHub Actions
+# https://docs.github.com/fr/code-security/dependabot/working-with-dependabot/keeping-your-actions-up-to-date-with-dependabot
+version: 2
+updates:
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      # Check for updates to GitHub Actions every week
+      interval: "weekly"

.github/workflows/build.yml

@@ -1,6 +1,11 @@
 name: Build image
 on:
   push:
+    branches:
+      - main
+    paths-ignore:
+      - '**/README.org'
+      - '.github/dependabot.yml'
   workflow_dispatch:
   schedule:
     - cron: '0 6 * * *'  # every day at midnight