submodule: bump openthread from `20c9bcb` to `b301a4c`

[dependabot[bot]]

Bumps openthread from 20c9bcb to b301a4c.

Commits

• b301a4c [settings] reset the platform settings file descriptor once closed (#10512)
• 6f2d8b6 [spinel] add get iid method (#10516)
• 9b57797 github-actions: bump actions/checkout from 4.1.6 to 4.1.7 (#10517)
• 7887cc7 [spinel] fix hints of missing radio caps (#10507)
• f331472 [routing-manager] track peer BRs and their age from Network Data (#10485)
• b0790b3 [spinel] fix cmake source list for spinel_helper.cpp (#10515)
• See full diff in compare view

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