Add the FST GC unit tests to the CI

Introduction

At the moment, the FST garbage collector tests are not being included in our CI:

• https://gitlab.cern.ch/cta/CTA/-/blob/main/python/eosfstgcd/test_ctafstgcd.py

Objective

These tests should be covered in one of our CI stages.

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Note: Before implementing these changes, we should wait for this issue to be completed and closed: #421 (closed)