v6.5-v8.1: update download URL from pingcap.org to pingcap.com (#22241)#22279

ti-chi-bot[bot] merged 1 commit intopingcap:release-6.5pingcap/docs:release-6.5from

ti-chi-bot:cherry-pick-22241-to-release-6.5ti-chi-bot/docs:cherry-pick-22241-to-release-6.5Copy head branch name to clipboard