Inacccurate test coverage visualization

This a follow-up from https://gitlab.com/gitlab-org/security/gitlab/-/merge_requests/4085#note_1932874973, where we noticed that the inline coverage visualization was flagging lines that did in fact have test coverage and were not uncovered in a way that would cause the undercoverage job to fail.

A check of the coverage.xml files shows that there was in fact a CI run with no coverage there, but not on the most recent pipeline.

More details in the linked security issue.