fix a wrong guide tip

[Hearen]

builder.getOutputStream().toString() will do the trick while builder.string() only prints the object reference (kind of address like "org.elasticsearch.common.xcontent.XContentBuilder@66e889df")

[elasticmachine]

Pinging @elastic/es-docs

[elasticmachine]

Pinging @elastic/es-core-features

[cbuescher]

Hi @Hearen, thanks for spotting this, you are right, the string() method was removed from XContentBuilder so the docs need update. I tracked down the change to that removed the method to PR #28972 and it looks like calling the static Strings.toString(XContentBuilder xContentBuilder) helper in org.elasticsearch.common.Strings is now the preferred way of replacing the removed method. Would you mind changing your PR to that since its more succinct?

[cbuescher]

@Hearen thanks for the update, I will run our test suite (although this is a small docs patch) before merging.
@elasticmachine test this please

[cbuescher]

@elasticmachine update branch

[cbuescher]

@elasticmachine test this please

[cbuescher]

The failing docs checks cannot be run on 5.x because of some CI build changes that haven't been backported. Merging regardless since this change only concerns a docs code block that should not be run.