Pipelines failing on TestBuildMasking job

A TestBuildMasking is failing on all new pipelines run on or targeting master. This seems to be related to recently merged !2679 (merged).

Examples of failures can be seen at:

• https://gitlab.com/gitlab-org/gitlab-runner/-/jobs/1316241242#L470 - masking string missing ] in expected [MASKED]
• https://gitlab.com/gitlab-org/gitlab-runner/-/jobs/1316086233#L469 - expected string not masked at all
• https://gitlab.com/gitlab-org/gitlab-runner/-/jobs/1316187722 - expected string not masked at all