ci: add node v20 to matrix (#4)

why
- wikimedia uses node v20

what
- add node v20 to matrix

Author: NovemLinguae

.github/workflows/test.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [14.x, 16.x, 18.x]
+        node-version: [14.x, 16.x, 18.x, 20.x]
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v3