chore: replace deprecated PingCAP download domains

[wuhuizuo]

Summary

• replace deprecated download.pingcap.org references with download.pingcap.com
• replace deprecated charts.pingcap.org references with charts.pingcap.com where present
• keep the existing paths and protocols unchanged

Validation

• git diff --check
• verified no remaining download.pingcap.org / charts.pingcap.org references in the patched branch

[ti-chi-bot]

Adding the "do-not-merge/release-note-label-needed" label because no release-note block was detected, please follow our release note process to remove it.

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[ti-chi-bot]

This cherry pick PR is for a release branch and has not yet been approved by triage owners.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick:

1. It must be LGTMed and approved by the reviewers firstly.
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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign d3hunter for approval. For more information see the Code Review Process.
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[gemini-code-assist]

Code Review

This pull request updates several download URLs across documentation and scripts, migrating from the pingcap.org domain to pingcap.com. The review feedback correctly identifies opportunities to further improve security by switching from insecure http to https for these binary downloads, mitigating potential man-in-the-middle risks.

[gemini-code-assist]

For security and consistency with other links in this file (e.g., line 6), please use https instead of http for downloading binaries. Downloading over unencrypted HTTP is susceptible to man-in-the-middle attacks.

Suggested change

	* `bin/sync_diff_inspector` # can be downloaded from [tidb-enterprise-tools-latest-linux-amd64](http://download.pingcap.com/tidb-enterprise-tools-latest-linux-amd64.tar.gz) or build from [source code](https://github.com/pingcap/tidb-tools)
	* `bin/sync_diff_inspector` # can be downloaded from [tidb-enterprise-tools-latest-linux-amd64](https://download.pingcap.com/tidb-enterprise-tools-latest-linux-amd64.tar.gz) or build from [source code](https://github.com/pingcap/tidb-tools)

[gemini-code-assist]

Please use https instead of http for these download URLs to ensure secure transmission of binaries and maintain consistency with other parts of the codebase (e.g., dm/tests/tiup/lib.sh).

Suggested change

	sync_diff_inspector_download_url="http://download.pingcap.com/tidb-enterprise-tools-nightly-linux-amd64.tar.gz"
	mydumper_download_url="http://download.pingcap.com/tidb-enterprise-tools-latest-linux-amd64.tar.gz"
	sync_diff_inspector_download_url="https://download.pingcap.com/tidb-enterprise-tools-nightly-linux-amd64.tar.gz"
	mydumper_download_url="https://download.pingcap.com/tidb-enterprise-tools-latest-linux-amd64.tar.gz"

[ti-chi-bot]

@wuhuizuo: The following tests failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	a61f75c	link	true	/test pull-verify
pull-dm-integration-test	a61f75c	link	true	/test pull-dm-integration-test
pull-cdc-integration-pulsar-test	a61f75c	link	true	/test pull-cdc-integration-pulsar-test

Full PR test history. Your PR dashboard.

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