Change node build targets to latest LTS and current

As detailed on https://github.com/nodejs/release#release-schedule, the
release schedule has changed since this node.js.yml workflow has last
been touched. 18.x will expire in October this year 2023. 14.x has been
EOL'd in 2021-10-19.

.github/workflows/node.js.yml

@@ -17,7 +17,7 @@ jobs:
 
         strategy:
             matrix:
-                node-version: [14.x]
+                node-version: [18.x, 20.x]
                 # See supported Node.js release schedule at https://nodejs.org/en/about/releases/
 
         steps: