fix(gitlab): Change instructions to uncheck expire tokens

[manuzope]

Previously, Gitlab tokens did not expire.

Now, by default, they do expire in 2 hours: https://gitlab.com/gitlab-com/www-gitlab-com/-/merge_requests/89791/diffs

We don't correctly support expiring Gitlab tokens right now.

So changing the instructions for Gitlab until we fix this (there is a ticket in the backlog) cause it's causing broken installations right now: #29010.

Before

After

How did I test this change

1. Created a new application with "Expire access tokens" checked
2. Made sure my local Sentry could communicate with it by fetching repositories
3. Waited for 2 hours
4. Tried to fetch repositories again but got a 401 from Gitlab
5. Created a new application with "Expire access tokens" unchecked
6. Repeated steps 2 & 3
7. Tried to fetch repositories again and was successful