CI: remove retry from jobs (#11899)

Since e8ee42280 (CI: remove deletion tasks of 'packet' VMs, 2024-09-13),
our tests appears to not be flakey anymore.
The current retry slow down the testing feedback on pull request.

Since it's not needed anymore, don't retry and fail fast.

.gitlab-ci.yml

@@ -55,7 +55,6 @@ before_script:
 
 .testcases: &testcases
   extends: .job-moderated
-  retry: 1
   interruptible: true
   before_script:
     - update-alternatives --install /usr/bin/python python /usr/bin/python3 1