submodule: bump openthread from `fab2c9a` to `7a2983b`

[dependabot[bot]]

Bumps openthread from fab2c9a to 7a2983b.

Commits

• 7a2983b [docs] add TREL config group (#9791)
• 7761b81 [cli] use static constexpr for constants instead of of enum (#9789)
• 84e0e77 [radio] add API for resetting CSL parameters (#9772)
• See full diff in compare view

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