fix(browser): always define commands (#8626)

Author: sheremet-va

packages/vitest/src/node/config/resolveConfig.ts

@@ -735,6 +735,7 @@ export function resolveConfig(
     ??= options.fileParallelism ?? mode !== 'benchmark'
   // disable in headless mode by default, and if CI is detected
   resolved.browser.ui ??= resolved.browser.headless === true ? false : !isCI
+  resolved.browser.commands ??= {}
   if (resolved.browser.screenshotDirectory) {
     resolved.browser.screenshotDirectory = resolve(
       resolved.root,