submodule: bump openthread from `67b8f5c` to `f12dfaf`

[dependabot[bot]]

Bumps openthread from 67b8f5c to f12dfaf.

Commits

• f12dfaf [coap] ensure CoAP header and token length are validated (#10720)
• 4a57dd8 [include] fix #include style for public OT headers (#10710)
• 94a6bfa [mle] replace "FED" with "FTD child" when applicable (#10718)
• 75ffb48 [tcat] TCAT documentation cleanup. (#10681)
• d60ec88 [mesh-forwarder] use Array to track forwarded frame info (#10540)
• 9d8fcfd [mesh-forwarder] simplify logging messages (#10716)
• See full diff in compare view

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