Prevent builtin extensions from being updated

Updating builtin extensions from the marketplace prevents us from patching them
(for example out GitHub authentication patches).

Index: code-server/lib/vscode/src/vs/workbench/contrib/extensions/browser/extensionsWorkbenchService.ts
===================================================================
--- code-server.orig/lib/vscode/src/vs/workbench/contrib/extensions/browser/extensionsWorkbenchService.ts
+++ code-server/lib/vscode/src/vs/workbench/contrib/extensions/browser/extensionsWorkbenchService.ts
@@ -206,6 +206,9 @@ export class Extension implements IExten
 		if (!this.gallery || !this.local) {
 			return false;
 		}
+		if (this.type !== ExtensionType.User) {
+			return false;
+		}
 		if (!this.local.preRelease && this.gallery.properties.isPreReleaseVersion) {
 			return false;
 		}
@@ -1057,6 +1060,10 @@ export class ExtensionsWorkbenchService
 				// Skip if check updates only for builtin extensions and current extension is not builtin.
 				continue;
 			}
+			if (installed.type !== ExtensionType.User) {
+				// Never update builtin extensions.
+				continue;
+			}
 			if (installed.isBuiltin && !installed.local?.identifier.uuid) {
 				// Skip if the builtin extension does not have Marketplace id
 				continue;