Update vscode-ci workflow to use Node.js 20

- Changes vscode-ci.yml matrix from node-version [18] to [20]
- Resolves undici v7.13.0 compatibility issue in PR workflows
- Aligns PR workflow with nightly workflow Node.js version
- Fixes vsce packaging failure: 'File is not defined' error

Author: gavindidrichsen

.github/workflows/vscode-ci.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        node-version: [18]
+        node-version: [20]
         os: [ubuntu-latest, windows-latest, macos-latest]
 
     steps: