Add forward progress update to NEWS.md (#54089)

Closes #40009 which was left open because of the needs news tag.

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Co-authored-by: Ian Butterworth <[email protected]>

Author: LilithHafner

NEWS.md

@@ -37,6 +37,10 @@ Language changes
    expression within a given `:toplevel` expression to make use of macros
    defined earlier in the same `:toplevel` expression. ([#53515])
 
+ - Trivial infinite loops (like `while true; end`) are no longer undefined
+   behavior. Infinite loops that actually do things (e.g. have side effects
+   or sleep) were never and are still not undefined behavior. ([#52999])
+
 Compiler/Runtime improvements
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