Fix YAML syntax in CI workflow

Author: sungshik

.github/workflows/build.yaml

@@ -24,7 +24,7 @@ jobs:
           distribution: 'temurin'
           cache: 'maven'
       - uses: actions/setup-node@v4
-          node-version: '20'
+          node-version: 20
           cache: 'npm'
       - name: install-tokenizer
         working-directory: rascal-textmate-core