fix(cli): don't override config by setting cli options to undefined (#2330)

This has been introduced by #2180. The change there will *always* set
argv.dir, no matter if it's been there before or not. When it's not
there, it will set it to undefined, which then will lead to vitest using
the root as fallback instead of the config set in the config file, since
CLI options override config options.

In our case, this config was essentially ignored since 0.24.4.

```js
import { defineConfig } from "vite"

export default defineConfig({
  test: {
    dir: "spec/javascript"
  }
})
```

with the only workaround of providing `dir` via CLI option.

Author: rmehner

packages/vitest/src/node/cli.ts

@@ -103,9 +103,15 @@ async function typecheck(cliFilters: string[] = [], options: CliOptions = {}) {
 }
 
 function normalizeOptions(argv: CliOptions): CliOptions {
-  argv.root = argv.root && normalize(argv.root)
-  argv.config = argv.config && normalize(argv.config)
-  argv.dir = argv.dir && normalize(argv.dir)
+  if (argv.root)
+    argv.root = normalize(argv.root)
+
+  if (argv.config)
+    argv.config = normalize(argv.config)
+
+  if (argv.dir)
+    argv.dir = normalize(argv.dir)
+
   return argv
 }