Merge pull request storybookjs#30134 from storybookjs/kasper/use-inst…

…alled-version-vitest

Addon Test: Always use installed version of vitest

code/addons/test/src/postinstall.ts

@@ -56,8 +56,7 @@ export default async function postInstall(options: PostinstallOptions) {
   const allDeps = await packageManager.getAllDependencies();
   // only install these dependencies if they are not already installed
   const dependencies = ['vitest', '@vitest/browser', 'playwright'].filter((p) => !allDeps[p]);
-  const vitestVersionSpecifier =
-    allDeps.vitest || (await packageManager.getInstalledVersion('vitest'));
+  const vitestVersionSpecifier = await packageManager.getInstalledVersion('vitest');
   const coercedVitestVersion = vitestVersionSpecifier ? coerce(vitestVersionSpecifier) : null;
   // if Vitest is installed, we use the same version to keep consistency across Vitest packages
   const vitestVersionToInstall = vitestVersionSpecifier ?? 'latest';