[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/spellcheck.yaml

@@ -21,7 +21,7 @@ jobs:
       - name: Set up Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: "22"
+          node-version: lts/*
           check-latest: true
           cache: "npm"
       - name: Install dependencies