refactor: remove node version matrix from CI test job

Author: tacxou

.github/workflows/ci.yml

@@ -16,10 +16,6 @@ jobs:
   test:
     runs-on: ubuntu-latest
 
-    strategy:
-      matrix:
-        node-version: [18.x, 20.x]
-
     steps:
       - name: Checkout code
         uses: actions/checkout@v4