CI: upgrade NodeJS (14.x → 20.x)

It's time to move to the active LTS version: NodeJS 20.

Author: Vimux

.github/workflows/ci-test.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       matrix:
         node:
-          - '14.x'
+          - '20.x'
 
     steps:
       - uses: actions/checkout@v3