[workflow] Use LTS node version and split "Run test" step (#3767)

Two small changes to the workflows:

- Run linter and spellcheck workflows with LTS node version. The
advantage of this is that we no longer have to raise the node version
for them.
- Split "Run test" step into two steps for more clarity.

.github/workflows/automated-tests.yaml

@@ -22,7 +22,7 @@ jobs:
       - name: "Use Node.js"
         uses: actions/setup-node@v4
         with:
-          node-version: 23
+          node-version: lts/*
           cache: "npm"
       - name: "Install dependencies"
         run: |
@@ -55,13 +55,15 @@ jobs:
       - name: "Install MagicMirror²"
         run: |
           node --run install-mm:dev
-      - name: "Run tests"
+      - name: "Prepare environment for tests"
         run: |
           # Fix chrome-sandbox permissions:
           sudo chown root:root ./node_modules/electron/dist/chrome-sandbox
           sudo chmod 4755 ./node_modules/electron/dist/chrome-sandbox
           # Start labwc
           WLR_BACKENDS=headless WLR_LIBINPUT_NO_DEVICES=1 WLR_RENDERER=pixman labwc &
-          export WAYLAND_DISPLAY=wayland-0
           touch css/custom.css
+      - name: "Run tests"
+        run: |
+          export WAYLAND_DISPLAY=wayland-0
           node --run test