Roll engine a71609f0695c..56d8634c51ff (2 commits) (#29185)

https://github.com/flutter/engine/compare/a71609f0695c...56d8634c51ff

git log a71609f0695c2977ac96b7a79e67e24767abfda2..56d8634c51ff50534b1853b71205eff861131dcf --no-merges --oneline
56d8634c5 Improve shadow doc in PhysicalShapeLayer (flutter/engine#8114)
bd0f9085e Adds a platfromViewId to SemanticsNode (flutter/engine#8055)

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bin/internal/engine.version

-a71609f0695c2977ac96b7a79e67e24767abfda2
+56d8634c51ff50534b1853b71205eff861131dcf