PR: test with node.js 18.x

As per https://github.com/nodejs/release#release-schedule node.js 16.x
is only in maintenance mode. Prior to switching over this here GitHub
App from node.js 16.x to 18.x, make sure that it actually works with
that node.js version.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.github/workflows/pr.yml

@@ -6,6 +6,9 @@ jobs:
   check:
     runs-on: ubuntu-latest
     steps:
+      - uses: actions/setup-node@v3
+        with:
+          node-version: 18
       - uses: actions/checkout@v3
       - name: npm install
         run: npm install