test: use CODE_VERSION for testing

release-nightly.yml uses 'insiders' release.
See https://github.com/microsoft/vscode-test for the usage.

Updates #1191

Change-Id: Id7225ac7abee545f037fde84016741656d2dfa33
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/290110
Trust: Hyang-Ah Hana Kim <hyangah@gmail.com>
Run-TryBot: Hyang-Ah Hana Kim <hyangah@gmail.com>
TryBot-Result: kokoro <noreply+kokoro@google.com>
Reviewed-by: Suzy Mueller <suzmue@golang.org>
diff --git a/test/runTest.ts b/test/runTest.ts
index 60d9601..96d3c27 100644
--- a/test/runTest.ts
+++ b/test/runTest.ts
@@ -11,6 +11,8 @@
 
 	let failed = false;
 
+	const version = process.env.CODE_VERSION || undefined;
+
 	try {
 		// The path to the extension test script
 		// Passed to --extensionTestsPath
@@ -18,6 +20,7 @@
 
 		// Download VS Code, unzip it and run the integration test
 		await runTests({
+			version,
 			extensionDevelopmentPath,
 			extensionTestsPath,
 			launchArgs: [
@@ -38,6 +41,7 @@
 		// tslint:disable-next-line:max-line-length
 		// https://github.com/microsoft/vscode/blob/890f62dfd9f3e70198931f788c5c332b3e8b7ad7/src/vs/workbench/services/workspaces/browser/abstractWorkspaceEditingService.ts#L281
 		await runTests({
+			version,
 			extensionDevelopmentPath,
 			extensionTestsPath: path.resolve(__dirname, './gopls/index'),
 			launchArgs: [