Add GHA config for Dependabot

* Upgrade `deploy-docs.yml` to the latest reusable workflows

(cherry picked from commit 3cad9e9f0f)

.github/dependabot.yml

@@ -23,3 +23,14 @@ updates:
          - "org.awaitility:awaitility"
          - "com.google.code.findbugs:jsr305"
          - "org.springframework.boot*"
+
+  - package-ecosystem: "github-actions"
+    directory: "/"
+    schedule:
+      interval: "weekly"
+      day: "saturday"
+    labels: ["type: task"]
+    groups:
+      development-dependencies:
+        patterns:
+          - "*"

.github/workflows/deploy-docs.yml

@@ -16,4 +16,4 @@ permissions:
 jobs:
   dispatch-docs-build:
     if: github.repository_owner == 'spring-projects'
-    uses: spring-io/spring-github-workflows/.github/workflows/spring-dispatch-docs-build.yml@v2
+    uses: spring-io/spring-github-workflows/.github/workflows/spring-dispatch-docs-build.yml@main