Fix regression introduced in #337

[d8vjork]

We cannot upgrade Inertia from 4.5.0 to 5.x as this introduces a new issue on our software.

Issue

Scenario

This is a piece of what we've in our app/Providers/RouteServiceProvider.php

   /**
     * These namespaces is applied to your controller routes.
     *
     * In addition, it is set as the URL generator's root namespace.
     *
     * @var array
     */
    protected $namespaces = [
        'web' => 'App\Http\Controllers',
        'api' => 'App\Http\Controllers\Api',
    ];

    /**
     * Define your route model bindings, pattern filters, etc.
     *
     * @return void
     */
    public function boot()
    {
        $this->configureRateLimiting();
        $this->configureRoutePatters();

        $this->routes(function () {
            Route::middleware('web')
                ->namespace($this->namespaces['web'])
                ->group(base_path('routes/web.php'));

            Route::prefix('api')
                ->middleware('api')
                ->namespace($this->namespaces['api'])
                ->group(base_path('routes/api.php'));
        });
    }

So having this namespace customised for our web.php routes file generates this issue of Laravel not detecting that the Inertia route controller from the macro its actually relative and not absolute as it was before.

This could also happen with anything that modifies the namespace like route groups, etc. So I think is better having this as a string.

[reinink]

Hey thanks so much for this PR. I just bumped into this myself tonight, so I fixed it (e026fe8), but now I'm realizing that you already submitted a fix 🤦‍♂️

Thanks so much either way for this! I hope to get this released soon.

[d8vjork]

@reinink Lovely! I was waiting using a forked for my company project, now we can go again to this