Remove hardcoded gitlab.com certificate

What does this MR do?

There are some tests that rely on validating gitlab.com TLS certificate. The certificate was hardcoded in the repository and then it has to be changed once expired on gitlab.com

This MR fetches the certificate in use at the moment when the tests are run.

Why was this MR needed?

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

Closes #2815