PlantUML is not parsing ReSTRUCTURED files

Summary

GitLab self-manages instance running

Steps to reproduce

1. Follow these steps:
2. Configure your PlantUML server. The Docker image suffices.
3. Enable the integration.
4. Create a new .rst file with the following contents:

  .. plantuml::
  
     Bob -> Alice: hello
     Alice -> Bob: hi

Open the file in GitLab.

Example Project

https://gitlab.com/customer-issue-reproduction/zd-271524

What is the current bug behavior?

A parsed ReSTRUCTURED file is displayed, while the plantuml directive is ignored:

What is the expected correct behavior?

The parsed file, including a parsed UML diagram, is displayed. Mockup: