chore: add VERSION check in build-vscode.sh

[jsjoeio]

This adds a check to ensure VERSION is set if running build:vscode locally.

Fixes #5795

[github-actions]

✨ code-server dev build published to npm for PR #5823!

• Last publish status: success
• Commit: 7f9df15

To install in a local project, run:

npm install @coder/code-server-pr@5823

To install globally, run:

npm install -g @coder/code-server-pr@5823

[codecov]

Codecov Report

Merging #5823 (7f9df15) into main (2cbb113) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5823   +/-   ##
=======================================
  Coverage   72.66%   72.66%           
=======================================
  Files          30       30           
  Lines        1683     1683           
  Branches      370      370           
=======================================
  Hits         1223     1223           
  Misses        397      397           
  Partials       63       63           

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[Kira-Pilot]

✅