chore(deps): update tidb-dashboard to eliminate vulnerable JWT dependency

[JmPotato]

What problem does this PR solve?

Issue Number: close #10109.

What is changed and how does it work?

Update tidb-dashboard to [121f017](https://github.com/pingcap/tidb-dashboard/commit/121f017c2150ec1037199e18e5f255aac057d48f) to eliminate vulnerable `golang-jwt/jwt` dependency.

Check List

Tests

• Unit test
• Integration test

Release note

None.

[ti-chi-bot]

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[ti-chi-bot]

@JmPotato: 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-unit-test-next-gen-3	6a292dc	link	true	/test pull-unit-test-next-gen-3
pull-unit-test-next-gen-1	6a292dc	link	true	/test pull-unit-test-next-gen-1
pull-unit-test-next-gen-2	6a292dc	link	true	/test pull-unit-test-next-gen-2

Full PR test history. Your PR dashboard.

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[rleungx]

Is it expected?