ci: use dependabot also for actions and run it daily

Also set the default commit-message format so it is the same format over
all repositories.

.github/dependabot.yml

@@ -3,4 +3,14 @@ updates:
   - package-ecosystem: "pip"
     directory: "/"
     schedule:
-      interval: "weekly"
+      interval: "daily"
+    commit-message:
+      prefix: "chore"
+      include: "scope"
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "daily"
+    commit-message:
+      prefix: "ci"
+      include: "scope"