[DOCS] https://firebase.google.com/docs/firestore/solutions/presence#updating_globally not correct example

https://firebase.google.com/docs/firestore/solutions/presence#updating_globally

Updating Cloud Firestore globally example is not correct and same as another example below

Open the linked Firestore presence documentation and compare the “Updating Cloud Firestore globally” example with the example immediately below. Confirm which content is duplicated or incorrect, then update the documentation so the global-update example is distinct and accurate.

Written by the indexing model from the issue text.