gitlab-advanced-sast-cpp: investigate possible flaky tests

Problem to solve

We may have flaky tests in https://gitlab.com/gitlab-org/security-products/analyzers/clangsa

See gitlab-org/security-products/analyzers/clangsa!48 (comment 2811693257)

Proposal

• investigate
• fix

reference

https://gitlab.com/gitlab-org/security-products/analyzers/clangsa/-/jobs/11671447271