fix(npm): use correct flags and update version for npm (#5533)

* fix: update npm-postinstall.sh script

Add --legacy-peer-deps to deal with weird npm issue with vscode
dependencies.

See: https://stackoverflow.com/a/66620869/3015595

* fix: use npm in release-standalone

* chore: update package.json

* chore: bump plugin engine for tests

package.json

@@ -1,7 +1,7 @@
 {
   "name": "code-server",
   "license": "MIT",
-  "version": "4.6.1",
+  "version": "4.6.1-1",
   "description": "Run VS Code on a remote server.",
   "homepage": "https://github.com/coder/code-server",
   "bugs": {