v6.5-v8.1: update download URL from pingcap.org to pingcap.com (#22241)#22282

ti-chi-bot[bot] merged 2 commits intopingcap:release-8.1pingcap/docs:release-8.1from

ti-chi-bot:cherry-pick-22241-to-release-8.1ti-chi-bot/docs:cherry-pick-22241-to-release-8.1Copy head branch name to clipboard