gitlab WebHook messages are not displayed correctly

Description:

Since the upgrade from 3.9 to 3.12, the display of Gitlab notifications are somewhat not correctly displayed.
It is probably linked to https://github.com/RocketChat/Rocket.Chat/issues/21009 but the behavior is different, and still somewhat incorrect. We never tried the 3.10 version of Rocket.chat.

Steps to reproduce:

1. Create an incoming integration in rocketchat (without any script)
2. Create a webhook in gitlab (version 13.9.x)
3. Fire the webhook in gitlab (push, commit, etc.)

Expected behavior:

Here is what used to be like :

Actual behavior:

And now :

Server Setup Information:

• Version of Rocket.Chat Server: 3.12.1
• Operating System: Centos 7
• Deployment Method: npm
• Number of Running Instances: 1
• DB Replicaset Oplog: enabled
• NodeJS Version: v12.18.4
• MongoDB Version: 3.6.3

Client Setup Information

• Desktop App or Browser Version: tried on native app, firefox, chrome
• Operating System: Windows 10

Relevant logs:

Logs are empty

Start by reproducing the display problem with a Rocket.Chat incoming integration and a GitLab 13.9.x webhook, following the listed push or commit steps. Compare the current output with the expected and actual screenshots, and review the related issue #21009 for context. Done means GitLab webhook notifications render correctly again without empty logs.