owner: fix data race on ownerManager.campaignCancel (#56362)#57132

ti-chi-bot[bot] merged 2 commits intopingcap:release-7.5pingcap/tidb:release-7.5from

ti-chi-bot:cherry-pick-56362-to-release-7.5ti-chi-bot/tidb:cherry-pick-56362-to-release-7.5Copy head branch name to clipboard