ci: test against ESLint v9

Author: G-Rath

.github/workflows/verifications.yml

@@ -35,7 +35,21 @@ jobs:
       matrix:
         # The .x indicates "the most recent one"
         node: [19.x, 18.x, 17.x, 16.x, 14.x, 14.17.0, 12.x, 12.22.0]
-        eslint: [7.5, 7, 8]
+        eslint: [7.5, 7, 8, 9]
+        exclude:
+          # eslint@9 doesn't support < Node v18
+          - node-version: 17.x
+            eslint-version: 9
+          - node-version: 16.x
+            eslint-version: 9
+          - node-version: 14.x
+            eslint-version: 9
+          - node-version: 14.17.0
+            eslint-version: 9
+          - node-version: 12.x
+            eslint-version: 9
+          - node-version: 12.22.0
+            eslint-version: 9
     steps:
       - name: Checkout
         uses: actions/checkout@v4