(doc): fix an incorrect snippet

[thammarith]

For auth_set_language_code.js, the snippet for version 9 is incorrect. Presumably, it took the version 8's and hasn't been updated to correctly reflect version 9.

To use the device's language, useDeviceLanguage() has to be called directly from auth not firebase.auth() like version 8.

import { getAuth } from "firebase/auth";

const auth = getAuth();
auth.languageCode = 'it';
// To apply the default browser preference instead of explicitly setting it.
- // firebase.auth().useDeviceLanguage();
+ // auth.useDeviceLanguage();

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[thatfiredev]

@thammarith Thanks for finding this and putting up a PR! :)

As noted at the top, this file is auto-generated from auth-next/index.js. Can you please edit that file instead? And after editing, please run npm run snippets to regenerate the appropriate files. https://github.com/firebase/snippets-web/blob/1fd0e3fbfc0d1bb56120fe1a4b75f85e44225dee/snippets/auth-next/index/auth_set_language_code.js#L1-L5

[thatfiredev]

Hey @thammarith Just checking in on this

[thatfiredev]

This has been fixed in #352