submodule: bump openthread from `b0790b8` to `a225ee9`

[dependabot[bot]]

Bumps openthread from b0790b8 to a225ee9.

Commits

• a225ee9 [test] add missing platform APIs in FakePlatform (#10844)
• 31f92b6 [mle] fix updating of mDataRequestState for Network Data (#10841)
• 230c155 [test] add retain_active_session option for ePSKc deactivate API (#10829)
• 4cc1ffd [dns-client] Initialize mSendLink structure in Client constructor (#10840)
• See full diff in compare view

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[dependabot[bot]]

Superseded by #822.