NEWS: add news for task-local RNG split change (#49217)

Author: StefanKarpinski

NEWS.md

@@ -7,6 +7,7 @@ New language features
 Language changes
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+* When a task forks a child, the parent task's task-local RNG (random number generator) is no longer affected. The seeding of child based on the parent task also takes a more disciplined approach to collision resistance, using a design based on the SplitMix and DotMix splittable RNG schemes ([#49110]).
 
 Compiler/Runtime improvements
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