submodule: bump openthread from `0d5f41d` to `d6eb56c`

[dependabot[bot]]

Bumps openthread from 0d5f41d to d6eb56c.

Commits

• d6eb56c [routing-manager] enhance TestPrefixStaleTime() (#10342)
• 18f7bc3 [mle] add TxMessage::AppendActiveAndPendingTimestampTlvs() (#10341)
• b776454 [mle] add Mle::TxMessage::AppendDatasetTlv() (#10340)
• b5b17ba [mle] allow appending pending timestamp TLV with zero seconds (#10327)
• fcd3c5c [timestamp] add IsValid() and comparison operator overloads (#10325)
• 5bb3667 [dataset] add WriteTimestamp() and RemoveTimestamp() (#10333)
• See full diff in compare view

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