Improve CI access (read-only), add dependabot for GH actions

Author: cowtowncoder

.github/dependabot.yml

@@ -0,0 +1,6 @@
+version: 2
+updates:
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"

.github/workflows/main.yml

@@ -18,6 +18,9 @@ on:
     paths-ignore:
     - "README.md"
     - "release-notes/*"
+permissions:
+  contents: read
+
 jobs:
   build:
     runs-on: ${{ matrix.os }}