fix(backups): a MariaDB restore can pin a dump another overlapping run uploaded #5319

A MariaDB restore trusts the dump name recorded on the Backup and checks only that the object exists (internal/backupcontroller/mariadbstrategy_controller.go, the restore path added in #5227). The probe that records the name lets only finished runs contest the attribution. So when two backup runs of one application overlap, a dump uploaded by the run that was still unfinished at probe time can be recorded as this Backup's dump, and the restore then pins it without the BestEffortDump warning.

This is not a regression: before #5227 the restore took the newest dump in that case too. The delete path already handles it: contestedMariaDBDump in mariadbstrategy_cleanup.go re-checks the recorded name against every run on the prefix.

Fix: run the same contest on restore, and when another run could own the dump, fall back to the best-effort path and raise the BestEffortDump warning.