test: await config update (#479)

Author: lukaszsamson

src/test/multiRoot/extension.test.ts

@@ -232,7 +232,7 @@ suite("Multi root workspace tests", () => {
   }).timeout(30000);
 
   test("extension starts first client on the same folder with mix.exs if useCurrentRootFolderAsProjectDir is true", async () => {
-    vscode.workspace
+    await vscode.workspace
       .getConfiguration("elixirLS")
       .update(
         "useCurrentRootFolderAsProjectDir",