Add NEWS entry for new default of BLAS threads

Author: giordano

NEWS.md

@@ -128,6 +128,9 @@ Standard library changes
   between different eigendecomposition algorithms ([#49355]).
 * Added a generic version of the (unblocked) pivoted Cholesky decomposition
   (callable via `cholesky[!](A, RowMaximum())`) ([#54619]).
+* On Linux, the number of default BLAS threads now respects process affinity,
+  instead of using total number of logical threads available on the system
+  ([#55574]).
 
 #### Logging