ci: do not test @testing-library/dom v9 against Node 12

Author: G-Rath

.github/workflows/validate.yml

@@ -25,6 +25,11 @@ jobs:
         testing-library: [8, 9]
         eslint: [6.8.0, 6, 7.0.0, 7, 8.0.0, 8]
         node: [12.22.0, 12, 14.17.0, 14, 16.0.0, 16]
+        exclude:
+          - testing-library: 9
+            node: 12.22.0
+          - testing-library: 9
+            node: 12
     runs-on: ubuntu-latest
     steps:
       - name: ⬇️ Checkout repo