test/integration: increase extension test timeout

Some tests (Test listPackages, Workspace Symbols) are slow
on windows CI.

Change-Id: Ieecae134ed9d459fad2bcd5d2c5daef41f579b0a
Reviewed-on: https://go-review.googlesource.com/c/vscode-go/+/251265
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
diff --git a/test/integration/extension.test.ts b/test/integration/extension.test.ts
index d16d35b..1b42970 100644
--- a/test/integration/extension.test.ts
+++ b/test/integration/extension.test.ts
@@ -40,7 +40,7 @@
 } from '../../src/util';
 
 suite('Go Extension Tests', function () {
-	this.timeout(10000);
+	this.timeout(15000);
 
 	const dummyCancellationSource = new vscode.CancellationTokenSource();