ci: add nodejs18 as it is released

Drop nodejs17 as it will be eol soon.

Author: abetomo

.github/workflows/tests.yml

@@ -9,7 +9,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [12.x, 14.x, 16.x, 17.x]
+        node-version: [12.x, 14.x, 16.x, 18.x]
         os: [ubuntu-latest, windows-latest, macos-latest]
 
     steps: