chore: adapt source code to newly introduced linting rules

VOOD-48

Author: arekisanda

src/test/runTest.ts

@@ -2,7 +2,7 @@ import * as path from 'path';
 
 import { runTests } from '@vscode/test-electron';
 
-async function main() {
+async function main(): Promise<void> {
   try {
     // The folder containing the Extension Manifest package.json
     // Passed to `--extensionDevelopmentPath`