chore: add dco check

[Syspretor]

Ⅰ. Motivation

Ⅱ. Modifications

Ⅲ. Does this pull request fix one issue?

fixes #XXXX

Ⅳ. List the added test cases (unit test/integration test) if any, please explain if no tests are needed.

Ⅴ. Describe how to verify it

VI. Special notes for reviews

Checklist

• Format your code make fmt.
• Add unit tests or integration tests.
• Update the documentation related to the change.

[gemini-code-assist]

Code Review

This pull request updates the pull request template by adding a checklist item for DCO sign-off. Feedback was provided to improve the terminology used for DCO signatures to avoid confusion with GPG signing and to correct the relative link path to the contributing documentation.

[gemini-code-assist]

There are two minor improvements for this new checklist item:

1. Terminology: Use "signed-off" instead of "signed". DCO (Developer Certificate of Origin) specifically uses the Signed-off-by trailer (added via git commit -s), whereas "signed" often implies GPG/SSH signatures (git commit -S). This aligns with the terminology used in CONTRIBUTING.md (e.g., line 104).
2. Link Path: Since this template is located in the .github/ subdirectory, the relative link to CONTRIBUTING.md should be ../CONTRIBUTING.md to ensure it works correctly when viewing the template file directly in the repository browser.

Suggested change

	- [ ] All commits are signed with DCO (`git commit -s`). See [Developer Certificate of Origin (DCO)](CONTRIBUTING.md#developer-certificate-of-origin-dco).
	- [ ] All commits are signed-off with DCO (`git commit -s`). See [Developer Certificate of Origin (DCO)](../CONTRIBUTING.md#developer-certificate-of-origin-dco).