Replace broken (possibly old?) Step #4

[chonghorizons]

Replace broken (possibly old?) Step #4 with a correct version from the completed example. No code added, just fixing an internal consistency on the page.

I've tested the completed example in Android Studio and it runs with no errors.

From the Cookbooks, so it's a high-visibility doc.
Fixes #3209

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[chonghorizons]

@googlebot I signed it!

@googlebot I signed it!

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[johnpryan]

LGTM, thanks!

[chonghorizons]

LGTM, thanks!

Actually, I think we might want to unmerge this pull request. Or the page needs some rewriting.

Now there is an inconsistency with the text in Step 4. (https://flutter.dev/docs/cookbook/navigation/navigate-with-arguments#4-navigate-to-the-widget)
It references pushNamed but the code I added didn't have used push.

And step 3 isn't in the completed example.

Someone (maybe me) should try to rewrite the page.

[johnpryan]

Thanks for pointing that out - creating an issue since this requires a bit more work: #3245