Type sharing test`Prototypes/ChangePrototype` is flaky on r1.8

CCRobot caught this on release1.8 branch;

```
[1192/2354 0.20] Failed -> Prototypes/ChangePrototype.js
out/Debug/ch -WERExceptionSupport -ExtendedErrorStackForTestHost -BaselineMode -maxInterpretCount:1 -maxSimpleJitRunCount:1 -bgjit- -dynamicprofilecache:profile.dpl.1466 -RecyclerVerifyMark -RecyclerConcurrentStress -VerifyBarrierBit -KeepRecyclerTrackData -trace:TypeShareForChangePrototype -JsBuiltIn- test/Prototypes/ChangePrototype.js
Output: (at line 28)
----------------------------
TypeSharing: Updating prototype object s DictionarySlot cache in __proto__.
----------------------------
Expected Output:
----------------------------
TypeSharing: Reusing prototype object s DictionarySlot cache in __proto__.
----------------------------
exit code: 0
```

Looks like Kunal had prepared the test and the bug fix associated with it almost a year ago. I'm going to assign myself for now and take a look.