Fix function name in refs code example

[fcallegari7]

The code example in docs/refs-and-the-dom is incorrectly calling a function from the previous code item.

This PR updates the method called from focusTextInput to focus, which is the method existent in the current object.

Currently in the website:

After the update:

[github-actions[bot]]

Size Changes

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This PR introduced no changes to the javascript bundle 🙌