Set dependency cooldown as a precaution against avoidable supply chain attacks

.github/workflows/ci.yml

@@ -187,3 +187,28 @@ jobs:
         with:
           modules-ignore: root_3 tests_3 smithy4sexample_3
           configs-ignore: test scala-tool scala-doc-tool test-internal
+
+  validate-steward:
+    name: Validate Steward Config
+    strategy:
+      matrix:
+        os: [ubuntu-22.04]
+        java: [temurin@11]
+    runs-on: ${{ matrix.os }}
+    steps:
+      - name: Checkout current branch (fast)
+        uses: actions/checkout@v6
+
+      - name: Setup Java (temurin@11)
+        id: setup-java-temurin-11
+        if: matrix.java == 'temurin@11'
+        uses: actions/setup-java@v5
+        with:
+          distribution: temurin
+          java-version: 11
+
+      - uses: coursier/setup-action@v1
+        with:
+          apps: scala-steward
+
+      - run: scala-steward validate-repo-config .scala-steward.conf

.scala-steward.conf

@@ -0,0 +1,3 @@
+updates.cooldown = {
+  minimumAge = "7 days"
+}