[12.x] Fix WithCachedConfig to work with parallel test runs

[cosmastech]

I'll be honest, I'm not entirely sure why this has fixed the problem described here. #57663 (comment) I've stepped through this many times and I am still lost about what this change is preventing from happening. I can see it has something to do with caching the config before calling the parallel testing provider, but... yeah, I'm still a touch confused.

For whatever it's worth, I thought that I wanted to set the application to cached before booting to avoid a disk read on LoadEnvironmentVariables, however, TIL that Env keeps a static instance of the environment variables stored. Turns out that wasn't necessary.

Thanks to @santigarcor for bringing this to my attention.

[SanderMuller]

@cosmastech I tried this change locally in our project, and it causes errors in some tests, for example a test that renders a page containing a NoCaptcha from the https://github.com/anhskohbo/no-captcha package.

Specifically on GuzzleHttp\Client::__construct(): Argument #1 ($config) must be of type array, null given from Anhskohbo\NoCaptcha\NoCaptchaServiceProvider::register()

    public function register()
    {
        $this->app->singleton('captcha', function ($app) {
            return new NoCaptcha(
                $app['config']['captcha.secret'],
                $app['config']['captcha.sitekey'],
                $app['config']['captcha.options']
            );
        });
    }

This test works fine with $this->markConfigCached($app);

[cosmastech]

@cosmastech I tried this change locally in our project, and it causes errors in some tests, for example a test that renders a page containing a NoCaptcha from the https://github.com/anhskohbo/no-captcha package.

Specifically on GuzzleHttp\Client::__construct(): Argument #1 ($config) must be of type array, null given from Anhskohbo\NoCaptcha\NoCaptchaServiceProvider::register()

    public function register()
    {
        $this->app->singleton('captcha', function ($app) {
            return new NoCaptcha(
                $app['config']['captcha.secret'],
                $app['config']['captcha.sitekey'],
                $app['config']['captcha.options']
            );
        });
    }

This test works fine with $this->markConfigCached($app);

Thanks for reporting this @SanderMuller. I will mark this as draft and continue my spelunking.

[cosmastech]

note: I think that this trait/approach needs refactored to work with multiple database connections. Currently, I don't believe that multiple connections are seeded/migrated. This approach is a little bit naive and assumes (like the rest of the parallel runner code) that there's but a single database to be concerned with.