chore(dashboard): update TiDB Dashboard to v7.5.5-a2486d76 [release-7.5]

[baurine]

What problem does this PR solve?

Issue Number: ref #4257 #8767

Update TiDB Dashboard to v7.5.5-a2486d76.

Release note

None

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[ti-chi-bot]

Hi @baurine. Thanks for your PR.

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[rleungx]

Does 7.1 or 8.1 need it?

[baurine]

Does 7.1 or 8.1 need it?

Clients are only required to fix in 6.5 and 7.5 currently, so I think we can fix it in 7.1 and 8.1 later if clients require.