ci: test against ESLint v9

Author: G-Rath

.github/workflows/verifications.yml

@@ -35,7 +35,21 @@ jobs:
       fail-fast: false
       matrix:
         node: [12.22.0, 12, 14.17.0, 14, 16, 17, 18, 19, 20, 22]
-        eslint: [7.5, 7, 8]
+        eslint: [7.5, 7, 8, 9]
+        exclude:
+          # eslint@9 doesn't support < Node v18
+          - node: 17
+            eslint: 9
+          - node: 16
+            eslint: 9
+          - node: 14
+            eslint: 9
+          - node: 14.17.0
+            eslint: 9
+          - node: 12
+            eslint: 9
+          - node: 12.22.0
+            eslint: 9
     steps:
       - name: Checkout
         uses: actions/checkout@v4