ci: test against all LTS versions

Author: lgutschow

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: ["20", "22"]
+        node-version: ["18", "20", "22"]
     steps:
       - uses: actions/checkout@v6