Four tests force a filesystem failure by freezing a directory to 0o555.
The CI container runs as root, mode bits do not constrain root, and the
rename those tests expect to fail succeeds — main has been red on
a_failed_rename_leaves_the_row_alone since the move-on-root-change work
landed, with nextest's fail-fast hiding the other three.
The guard probes the filesystem rather than the uid: what the tests
depend on is the refusal, and a container can hold CAP_DAC_OVERRIDE
without being uid 0.
Miguel Palhas
656ca6c259