build: update to node-v20 [skip ci]

.github/workflows/insider-spearhead.yml

@@ -38,7 +38,7 @@ jobs:
       - name: Setup Node.js environment
         uses: actions/setup-node@v4
         with:
-          node-version: '18'
+          node-version: '20.12'
 
       - name: Clone VSCode repo
         run: . get_repo.sh

.github/workflows/stable-spearhead.yml

@@ -33,7 +33,7 @@ jobs:
       - name: Setup Node.js environment
         uses: actions/setup-node@v4
         with:
-          node-version: '18'
+          node-version: '20.12'
 
       - name: Clone VSCode repo
         run: . get_repo.sh