Roll engine 76794745b676..876c4c339064 (4 commits) (#31231)

https://github.com/flutter/engine/compare/76794745b676...876c4c339064

git log 76794745b6764246cffafb237182f7fafeac41f8..876c4c339064ed321f37fba61422194d84cbfdb7 --no-merges --oneline
876c4c339 Assert that all VM launches in the process have the same opinion on whether the VM should be leaked in the process. (flutter/engine#8622)
72c84c287 Revert "Roll src/third_party/dart 7b9ab9f353..714a082a5d (7 commits)" (flutter/engine#8624)
f017fe74a Avoid manually shutting down engine managed isolates. (flutter/engine#8621)
80e934e32 Roll src/third_party/dart 7b9ab9f353..714a082a5d (7 commits)

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bin/internal/engine.version

-76794745b6764246cffafb237182f7fafeac41f8
+876c4c339064ed321f37fba61422194d84cbfdb7