Use @session directive for flash message example in redirecting.md

[sebdesign]

Review the contribution guide first at: https://livewire.laravel.com/docs/contribution-guide

1️⃣ Is this something that is wanted/needed? Did you create a discussion about it first?

No, this is a minor change in the docs.

2️⃣ Did you create a branch for your fix/feature? (Main branch PR's will be closed)

Yes: patch-1

3️⃣ Does it contain multiple, unrelated changes? Please separate the PRs out.

No.

4️⃣ Does it include tests? (Required)

No.

5️⃣ Please include a thorough description (including small code snippets if possible) of the improvement and reasons why it's useful.

The @session('status') directive is more straightforward than the @if (session('status')) expression.

Thanks for contributing! 🙌