submodule: bump openthread from `4e8f3c0` to `215c23f`

[dependabot[bot]]

Bumps openthread from 4e8f3c0 to 215c23f.

Commits

• 215c23f [diag] add diag output callback (#10354)
• 31e512a [mle] replace Mle::GetNextHop() with GetParentRloc16() (#10407)
• e581f07 [ip6] add Ip6::Address::IsLinkLocalUnicastOrMulticast() (#10405)
• 3345af0 [otci] fix the setDaemon() is deprecated warning (#10409)
• 4978e58 [otci] add ADB USB connection support for OTCI (#10406)
• See full diff in compare view

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